The Chemistry of Carbanions. VI. Stereochemistry of the Wittig

Wittig Reactions in Water Media Employing Stabilized Ylides with Aldehydes. Synthesis of α,β-Unsaturated Esters from Mixing Aldehydes, α-Bromoester...
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NOVEMBER, 1964

3327

WITTIGREACTION WITH STABILIZED YLIDS

B. Other Methods.-Similar runs were made where the proportions of reagents were varied (Table I) and where the solvent, metalation reagent, and alkyl nitrite were varied (Table 11). The product was isolated as in the preferred procedure. Other Preparations of Oximes.-The procedures employed were similar to the ones described above. The oximes listed in Table I11 were usually prepared in 50 ml. of anhydrous liquid ammonia from 0.1-mole quantities of sodium, reactant, and butyl nitrite in 10 ml. of ethyl ether. Some of the products were

sublimed a t 0.005 mm. Other exceptions are noted in the table. N.m.r. Spectra.-The spectra were determined with a Varian Model A-60 apparatus using deuteriochloroform or deuteriomethanol as solvent for the compounds and tetramethylsilane as the internal standard. Infrared Spectra.-The spectra were determined on each compound in a potassium bromide pellet with a Baird Model 4-55 apparatus.

The Chemistry of Carbanions. VI. Stereochemistry of the Wittig Reaction with Stabilized Y l i d s l " HERBERT 0. HOUSE,VERAK. JOSES,A N D GEORGE A. FRANK'^ Department of Chemistry, Massachusetts Institute of Technology, Cambridge 39, Massachusetts Received M a y 12, 1964 The effect of various reaction conditions on the proportions of cis and trans olefinic products 'obtained from the Wittig reaction of stabilized ylids 1 and 10 with acetaldehyde and chloroacetaldehyde has been studied. The highest proportion of cis isomer was obtained by the use of the protonic solvent, methanol. Solutions of lithium salts were less effective and suspensions of lithium salts were without effect in enhancing the proportion of cis olefin in these cases. Our study of the Wittig reaction of the benzylidene phosphorane 4 with propionaldehyde does not support the previous reports that the proportion of the cis isomer may be markedly enhanced by the presence of a suspension or a solution of lithium bromide or lithium iodide in the reaction mixture.

Earlier investigations2 of the Wittig reactions of aldehydes with ylids stabilized by the presence of carbonyl substituents at the a-position (e.g., 1) have indicated that the predominant stereoisomer in the olefinic product is that isomer in which the carbonyl substituent is trans to the larger group at the p-carbon atom (e.g., 2).

CHsCHO

(C&)aP

= CH-C02CH3 1

CHa

c/"

\C= / \

H

\

tained from n-butyllithium and hydrogen bromide or hydrogen iodide) and then with propionaldehyde, the proportion of the cis' stereoisomer 6 in the product was reported to be increased to over

+

COzCH3

/

H/c=c\H 3

Other studies of the stereochemistry of the Wittig reaction3r4have indicated that the degree of stereoselectivity observed is somewhat dependent on the- substituents present and is markedly influenced b y changes in the reaction medium. For example, the reaction of the benzylidene phosphorane 4 with propionaldehyde in benzene solution was found to yield a mixture of olefins 5 and 6 containing 26% of the cis isomer 6. However, if the solution of the ylid 4 was treated successively with a suspension of lithium bromide or lithium iodide (ob(1) (a) This research has been supported by grants from the National Science Foundation (Grant No. G-25214) and the National Institutes of Health (Grant No. RG-8761); (b) National Institutes of Health Predootoral Fellow, 1963-1964. (2) (a) S. Trippett, Quart. Reu. (London), 17, 406 (1963); (b) H. 0. House and G. H. Rasmusson, J . Ore. Chem., 16, 4278 (1961); (c) H. 0. House and H. Babad, ibid., 18, 90 (1963); (d) H. J. Bestmann and 0. Kratzer, Chem. Ber., 95, 1894 (1962); (e) R . Ketoham, D. Jambotkar, and L. Martinelli, J . Ore. Chem., 17, 4666 (1962); (f) A . J. Speziale and D. E. Biasing, J . A m . Chem. Soc., 85, 3878 (1963); (9) 5. Fliszar, R . F . Hudson, and G. Salvadori, Helv. Chim. Acta, 46, 1580 (1963). (3) (a) A. J. Speziale and K. W . Ratts. J . A m . Chem. Soc., 85, 2790 (1963); (b) C . F. Hauser, T . W. Brooks, M. L. Miles. M. A. Raymond, and G . B. Butler, J . Org. Chem., 18,372 (1963). (4) (a) L. D. Bergelson and M. M. Shemyakin, Tetrahedron, 19, 149 (1963); (b) L. D. Bergelson, V. A. Vaver. L. I. Barsukov, and M. M. Shemyakin. Izu. Akad. Nauk S S S R , Old. K h i m . Nauk. 1053 (1963); ( e ) L. D. Bergelson and M. M . Shemyakin, Angew. Chem., 76, 113 (1964).

CeHs

\

/CH2CH3

H,cd\H 6

These reports prompted us to explore the stereochemical changes which would result from changes in the medium employed for reactions of stabilized ylids with aldehydes since procedures allowing substantial change in the stereochemical composition of the product would have obvious synthetic utility. Also we hoped that working with stabilized ylids which could be isolated and purified prior, to reaction might offer some advantage in studying the previously reported4 medium effects. For this purpose we have studied the reaction of the ylid 1 with acetaldehyde and chloroacetaldehyde to form the esters 2 , 3, 7, and 8. The stereochemical outcome in the presence of a small amount of benzoic acid, a reported catalyst for the Wittig reaction,&was also explored.. The reaction of the phosphonate anion lo6 with acetaldehyde to form esters 2 and 3 was also examined a s well as the reaction of the ylid 11 with chloroacetaldehyde to form the unsaturated ketone 12. In the latter case, we were unsuccessful in efforts to determine the stereoselectivity of the reaction since only the tmns isomer 12 was isolated. For all of the (5) (a) C. Riiohardt, S. Eichler, and P . Panse, Angeu. Chem., Intern. E d . , Engl. I,619 (1963); (b) 9. Fliszar, R. F. Hudson, and G . Salvadori, Helu. Chim. Acta, 47, 159 (1964). (6) W. 5. Wadsworth and W. D. Emmons, J . A m . Chem. Soc., 88. 1733 (1961).

HOUSE,JONES, AND FRANK

3328

TABLEI SUMMARY OF THE INFLUEXCE OF THE REACTION MEDIUM ON THE STEREOSELECTIVITY OF THE WITTIQ REACTION WITH STABILIZED YLIDS

Reactants

Acetaldehyde

+

Solvents

Additives

CHzClz, DME,a ... or D M F b CHCla LiBr, suspension DMFb PhC02Hor KCI solution DMFb LiBr, LiC1, LiClO,, or Lix’08 solution DMFb HzO CHsOH , . . CHsOH LiNO3 or PhCO2H solution D M D or ,.. DMFb

1 1 1 1

1 1

1

10

Proportion of c i s isomer 3 or 8 in product, %

3-6 3 4 18-22

10-25 38 34-38

4-5

Chloroacetaldehyde

+

CH2C1,or DMFb DMFb

1 1

1 CHaOH 1,2-Dimethoxyethane.

...

LiBr, LiNO3, or LiClOl solution ...

b

17-29

31-34

52

Dimethylformamide.

other cases studied, appropriate control experiments demonstrated that the initially formed products were not isomerized by the conditions of the reactions and subsequent analyses. The results of these experiments, summarized in Table I, suggest the following concluClCHz

ClCB

>c=c / H H

>=C H

‘C02CHs

8

7

(CaHsO)*P=CH-

Na+

0-

\/C02CH3 H

COaCHs

9 0 9

(CsHs)3P= CH-CO-CHZCBHS 11

10

ClCHa

‘c=c

H/

/H ‘CO-CHGH~ 12

sions. (1) Polarity of the solvent (methylene chloride us. dimethylformamide) has much less influence on the stereoselectivity of the reaction than does the use of a protonic solvent (e.g., methanol), (2) Although lithium salts in solution have some effect on the stereoselectivity of the reaction, their effect at the concentrations used (0.3 to 1.0 M ) is not so great as the use of a protonic solvent. The efficacy of methanol and lithium salts added in comparable molar concentrations was not determined. However, the results obtained (Table 11)with added water or benzoic acid suggest that lithium salts would be more effective than an equimolar concentration of a proton-donating additive in enhancing the proportion of cis isomer in the product. (3) Use of a

VOL.29

suspended lithium salt was without effect and solutions of all lithium salts examined appeared to be equally effective irrespective of the nature of the anion (bromide, chloride, nitrate, or perchlorate). Although our finding that the use of protonic solvents enhances the proportion of the cis isomer in the olefinic product is in agreement with previous results4j7 obtained with the benzylidene phosphorane 4, the data we obtained when lithium salts were added to the reaction differed substantially from earlier reports4 in several respects. In particular our results suggested that the magnitude of this effect was less, not greater, than the effect of using protonic solvents, that lithium salts were only effective when in solution, not as suspensions, and that the effect was attributable to the lithium cation and not iodide or bromide anion as previously stated. In order to examine the possibility that the effect of lithium salts might be very different with the less stable ,~ benzylidene ylid 4 utilized in the previous ~ t u d i e s we have repeated the earlier study of the reaction of the ylid 4 with propionaldehyde. A summary of our results compared with the previously published results is presented in Table 111. The data will be noted to agree reasonably well except in cases where solutions or suspensions of lithium salts were involved. In no case of this type which we studied were we able to obtain the very high proportion of cis-1-phenylbutene previously r e p ~ r t e d . ~Subsequent correspondence has established that the previously product analyses were in error and recent data are more nearly in keeping with our results.* We believe the presently available data for ylids such as 1 and 4 are compatible with the idea that the proportion of the cis isomer is enhanced by the presence in the reaction solution of a Lewis acid such as a protondonating solvent or a lithium cation and are not consistent with the idea of a prior coordination of the ylid with a Lewis b a ~ e . ~Most , ~ studies with reactive ylids have utilized the reaction of phosphonium salts with organolithium reagents to form an ylid accompanied by a lithium salt whereas the stable ylids are usually isolated free from extraneous materials. Consequently our finding that added lithium salts appear t y h a v e more effect on the stereochemistry of reactions with the stabilized ylid 1 than with the ylid 4 may simply be a result of the fact that the ylid 4 was already contaminated with a substantial amount (see Experimental) of lithium salt formed during the preparation of the ylid. Both the catalysis of Wittig reactions of stabilized ylids by proton-donating solvents2f or additives6 and the enhanced proportions of cis isomer formed in the presence of dissolved Lewis acids (methanol, water, or (7) (a) G. Wittig and W. Haag, Chem. Ber., 88, 1054 (1955); (b) G. Drefahl, D. Lorenz. and G. Schnitt. J . prokt. Chem., [4] 98, 143 (1904). (8) We are indebted to Professor Shemyakin and Dr. Bergelson for repeating these experiments and informing us of the results. For reactions of the ylid 4 with propionaldehyde in benzene, the per cents of the c i e isomer 6 obtained were 20, 27, and 41 when the lithium salt present waa LiC1, LiBr, and LiI, respectively. In these cases, the lithium salt present was that formed by reaction of the appropriate phosphonium halide with butyllithium. The corresponding per cents of the et8 isomer 6 obtained in dimethylformamide solution were 73, 71, and 74. Since we do not know the amounts of the various lithium halides which were in solution (see the Experimental of this paper for data concerning the amount of chloride ion present in benzene solutions of the ylid 4) in the benzene experiments, the significance of the changes in isomer distribution with changes in the halide ion are not clear. However, these data, like ours, indicate that in dimethylformamide, where the lithium salts are in solution, changes in the anion do not, within experimental error, alter the proportion of the isomers produced.

WITTIGREACTION WITH STABILIZED YLIDS

SOVEMBER, 1964

REACTION OF

THE

TABLE I1 PHOSPHORANE 1 WITH ACETALDEHYDE

mmoles

Phosphorane 1. mmoles

Solvent (ml.)

Additive (mmoles)

4.3 5.5 4.3 4.3 4.3 4.3 4.3 4.3 4.3

0.97 9.1 1.06 0.90 1.04 1.10 0.95 0.96 1.20

CHzCL ( 3 DMEC(20) DMFd (3) MeOH (3-4) DMFd (3) DMFd (3) DMFd ( 5 ) DMFd (3) DMF~ (3)

...

4.3 4.3 4.3 4.3

0.90 1 .o 1.15 0.99

CHaCHO,

0.93 4.3 0.99 4.3 2.56 4.3 1.02 4.3 1.01 4.3 a The range of yields obtained. these average values by &a70 or and was used as a suspension.

70

Solvent

CsHs CsHa

... ...

DMFa DMFa

a

... LiBr or LiI suspension ... LiBr solution

CHsOH or ... CzHsOH Dimethylformamide.

R, FROM

REACTION OF

THE

H

PROPIONALDEHYDE

Additive

6b 3 3b 38b 20b

84-88" 90 95-98" 8C-96° 83-85a 75-82a 81 83 70

...

TABLE I11 WITH

v-Composition% cis 8 % tranu 4

Yield,

94b 97 97b 62b 80 82 78 78 80

LiBr (1.28) LiCl ( 1.24) Hb 22 LiBr (4.8) 22 LiC104 (0.90) 20 LiC104.3H20 (1.16) 38 62 LiN03 (7.4) 81 MeOH (3) 21 79 LiNOI (1.0) 87 DMFd ( 3 ) 4 96 DMFd (3) KC1 (0.88) 82 20 80 DMFd (3) MgBrP.6 H 2 0 74 (1.08) 10 90 HzO (0.95) 90 DMFd ( 3 ) 25 75 HzO (28) 63 DMFd (3) 3 97 CHCL ( 5 ) LiBr" (2.8) 64 4 96 PhCOzH (1.02) 85 DMFd ( 3 ) 34 66 PhCOZH (0.296) 83 NeOH (3) Average values from two or more experiments. The individual values obtained differed from Dimethylformarnide. e The salt was not soluble in chloroform 1,2-Dimethoxyethane. less.

STEREOCHEMICAL RESULTS OBT.4INED

YLID4

3329

,c=c,

/H COzCHs

Proportion of cis isomer -6 in product, %Found Ref. 4

23 23-25

26 91-93

4446 46 50-52

65 96 47

lithium salts) would appear to be explicable in terms of coordination of the Lewis acid with the carbonyl oxygen atom in the addition step6b as illustrated in structure 17. Such a process hasample analogy in theaddition of other nucleophiles to carbonyl functicns. The increased proportion of the cis isomer 16 formed under such circumstances would appear to be the result of one or both of the followingfactors. Interconversion of the two stereoisomeric solvated betaines 18 and 19 (either by reversal of the addition reactionzf or by way of an intermediate ylid resulting from loss of a proton from 18 or 1g2a) may be slower than the corresponding interconversion of the unsolvated betaines 13 and 14. If the relative rates of decomposition of betaines 13 or 19 to 15 and 14 or 18 to 16 remain unaltered, the result will be to make the reaction less stereoselective.9 Even if the rate of interconversion of the betaines is not retarded by solvation, the relative steady-state concentration of betaines 13 and 14 would be expected to differ from the corresponding concentrations for sol(9) J. N. Butler and G. J. Small [Can. J . Ckem., 41, 2492 (1963)l have reported t h e equilibrium between esters 4 and 8 in t h e gas phase t o correspond t o approximately 80% of the trans isomer. Our preparations in nonprotonic (95% trans) and protonic eolvents (62% trana) permit t h e preparation of samples with both more and less of the unstable isomer t h a n would be expected a t equilibrium.

13

19

ti

ti

14

/

\ 16

vated betaines 18 and 19. For electrostatic reasons, both betaines 13 and 14 would be expected to exist primarily in the indicated conformations. However, the solvated betaines 18 and 19 should have much less preference for corresponding conformations where the phosphorous and oxygen atoms are near one another because the negative charge remaining at the oxygen atom has been lessened substantially. Hence, for a combination of electrostatic and steric reasons, the betaine 13 (leading to trans olefin 15) is expected to be more stable than its isomer 14. However, the relative

HOUSE,JONES, A N D FRANK

3330

stabilities of solvated betaines 18 and 19 would be expected to be more nearly equal and may possibly favor the isomer 18 leading to cis olefin 16. Until kinetic data of the type previously obtained2' in nonprotonic solvents is also available for a comparable system in protonic solvents, a choice from among these possibilities cannot be made.

Experimental1o Preparation of the Ylids and Their Precursors.-Carbomethoxymethylenetriphenylphosphorane ( I ) , prepared as previously described,ll was obtained as fine, white prisms, m.p. 160-163" (lit." 162-163"), from an ethyl acetate-petroleum ether (b.p. 30-60') mixture. The material has strong infrared absorption12 a t 1620 em.-' (this peak is apparently characteristic of the system +P+C=C(O) -OR)2g3h,13and an n.m.r.14 multiplet in the region 6 7.2-8.0 (15H, aryl C-H) as well as a singlet a t 3.50 (3H, 0-CHI) and a broad peak centered at 3.20 (IH, >P+CHCO-). A mixture of 34.93 g. (0.22 mole) of triethyl phosphite and 32.75 g. (0.215 mole) of methyl bromoacetate was heated to 70100" for 6 hr. during which time ethyl bromide was allowed to distill from the mixture. Heating was continued for 8 hr. and then the mixture waa fractionally distilled under reduced pressure to separate 39.7 g. (867,) of methyl diethylphosphonoacetate as colorless fractions, b.p. 113-134" (9-13 mm.), n 2 4 ~1.43101.4320. One of the latter fractions, b.p. 127-134" (9 mm.) [lit.161316-132' (9 mm.)], n Z 41.4320, ~ was judged from its gas chromatogram16 to contain a t least 98y0 of the desired ester. The material has infrared absorption17 a t 1750 em.-' (ester C=O) with a set of overlapping n.m.r.17 quadruplets ( J = 7 c.p.5.) centered a t 6 4.13 and 4.27 (4H, two -OCHz-), a singlet a t 3.8 (3H, OCH,), a doublet ( J = 22 c.p.5.) centered a t 2.93 (2H, +P+CH2), and a triplet ( J = 7 c.p.5.) centered a t 1.37 (6H, two

CH3).

Anal. Calcd. for C7HlbOsP: C, 39.99; H, 7.19. Found: C, 39.95; H , 7.13. To an ethereal solution of 10.82 g. (0.07 mole) of phenylacetyl chloride was added, dropwise and with stirring, a cold (0') ethereal solution containing 0.14 mole of diazomethane. The resulting solution was allowed to stand overnight and was then treated with dry hydrogen chloride until the yellow color of the diazo ketone was discharged. After the ethereal solution had been washed with aqueous sodium bicarbonate, dried, and concentrated, distillation afforded 8.17 g. of a fraction, b.p. 110-118" (6 mm.), 1 2 2 5 ~ 1.5308,18 containing16 approximately 80% of 3chloro- 1-phenyl-2-propanone, the rem'ainder of the fraction being a mixture of methyl phenylacetate and ethyl phenylacetate. A solution of 8.43 g. (0.05 mole) of this crude chloro ketone and 13.1 g. (0.05 mole) of triphenylphosphine in 75 ml. of methylene chloride was stirred a t room temperature for 30 min. and then concentrated and mixed with ether. The crude salt which separated was collected and recrystallized from a methanol-ethyl acetate mixture to separate 12 g. (85%) of the salt as white needles, melting with decomposition over the range 153-200'. (10) All melting points are corrected and all boiling points are uncorrected. Unless otherwise stated magnesium sulfate was employed as a drying agent. The infrared spectra were determined with a Perkin-Elmer, Model 21, infrared recording spectrophotometer fitted with a sodium chloride prisni. The ultraviolet spectra were determined with a Cary recording spectrophotometer, Model 14. T h e n.m.r. spectra were determined a t 60 Mc. with a Varian, RIodel A-60, n.m.r. spectrometer. The mass spectra were obtained with a C E C , Model 21-130, mass spectrometer. T h e rnicroanalyses were performed by Dr. S. M. Nagy and his associates and by the Scandinavian Microanalytical Laboratory. (11) 0. M e r , H . Gutmann, M . Montavon. R . Riiegg. G. Ryser, a n d P. Zeller, Helv. Chim. Acta, 40, 1242 (1957). (12) Determined a s a solution in chloroform. (13) (a) F. Ramirea and 6 . Dershowita, J . Org. Chem., 21, 41 (1957); (b) A. J. Speziale and K . W. Ratts, ibid., 28, 465 (1963). (14) Determined as a solution in deuteriochloroform. (15) P. Nylen, Ber., 67, 1023 (1924). (16) A column packed with Dow Corning silicone fluid, No. 710. suspended on Chromosorb P was employed. (17) Determined as a solution in carbon tetrachloride. (18) W. D. McPhee and E . Klingsberg [ . I . A n . Chem. SOC.,66, 1132 ~ D for 3-chloro(1944)l report b.p. 130-133' (17 mm.) and T L ~ 1.5357-1.5361 1-phenyl-2-propanone.

VOL. 29

This 3-phenylacetonyltriphenylphosphoniumchloride apparently forms a series of solvates since repeated efforts to obtain an analytically pure sample were unsuccessful. A sample of the salt which had been crystallized several times from ether -methylene chloride mixtures and then dried a t 85" for several days melted with decomposition a t 204-207" and had a composition (Calcd. for C27H~4ClOP.0.5H 2 0 : C, 73.61; H, 5.73; C1, 8.06. Found: C, 73.65; H, 6.11; C1, 7.83.) suggesting that the material is a hemihydrate. The material has infrared absorption12 a t 1715 em.-' (ester C=Oj with n.m.r. absorptionI4 in the region 6 7.1-8.0 (20 H, aryl C-H) as well as a doublet ( J 12 c.P.s.) centered a t 6 6.26 (2H, +P+-CH2) and a broad peak a t 4.32 (2H, -COCHZCBHS). A suspension of 4.3 g. (0.01 mole) of this phosphonium salt in a mixture of 15 ml. of water and 12 ml. of methylene chloride was treated with sufficient 10% aqueous sodium hydroxide to make the aqueous layer alkaline. The organic layer was separated, washed with water, dried, and concentrated. Recrystalization of the residue (2.6 9.) from an ethyl acetate-methylene chloride mixture separated 2.38 g. (5873 oftheylid 11aswhiteneedles,m.p. 102-102.5'. TheproductexhibI ited a strong infrared band12 a t 1535 em. -1 + P + C H = C - 0 , 2 ~ , 3 a ~ 1 3 ultraviolet maxima18 a t 267 mp'(e 7560), 273 (7230), and 287 (6520), and an n.m.r.l4 multiplet in the region 6 7.1-7.9 (20H, aryl C-H) with a partially resolved multiplet (apparently an AB pattern superimposed on other absorption) in the region 6 3.4I 3.9 (3H, -CHZ and >P+CH=C-0). Anal. Calcd. for Cz7H23PO: C, 82.21; H, 5.88. Found: C, 82.24; H, 6.00. Benzyltriphenylphosphonium chloride, prepared as previously described,20separated from acetonitrile as fine, white crystals, m.p.325-330'dec. [lit. 285°,20314-31507].Then.m.r.spectrum14 of the product has a doublet ( J = 15 c.p.5.) centered a t 6 5.38 (2H, -CHzP't), a peak at 7.09 (5H, aryl C-H), and a multiplet in the region 7.5 to 7.9 (15H, aryl C-H). Anal. Calcd. for C25H22ClP: C, 77.20; H, 5.70. Found: C, 77.39; H, 5.74. Reaction of the Ylid 1 with Acetaldehyde .-Authentic samples of methyl trans-crotonate (2) and methyl cis-crotonate (3) were prepared by the previously describedz1pyrolysis of the crude pyrazoline, b.p. 67-72" (0.1 mm.) [lit.22140" (17 mm.)], 'obtained from methyl acrylate and diazomethane. Each of the desired isomers was separated from the product mixture2l by gas chromatography.23 The cis ester 3 (first eluted) exhibited a molecular ion peak a t m/e = 100 in its mass spectrum with infrared absorption17a t 1725 (conjugate ester C=O) and 1650 ern.-' (conjugate C=C) and n.m.r. absorption17attributable to the vinylic protons a t 6 6.25 (lH, a pair of overlapping quadruplets, J = 7 and 11 c.p.5.) and 5.73 ( l H , pair of quadruplets, J = 1.5 and 11 c.p.5.) as well as a singlet a t 3.61 (3H, OCH3) and a pair of doublets ( J = 1.5 and 7 c.p.8.) centered a t 2.10 (3H, CHIC).^^ The trans isomer 2, with a molecular ion peak at m / e * = 100 in its mass spectrum, has infrared absorption17 a t 1730 (conjugate ester C=O), 1660 (conjugate C=C), and 970 em.-' (trans CH=CH), with n.m.r. absorption1' attributable to the vinyl protons a t 6 6.87 ( l H , pair of overlapping quadruplets, J = 15.5 and 7 c.P.s.) and a t 5.76 ( l H , pair of quadruplets, J = 15.5 and 1.5 c.p.5.) aa well aa a singlet a t 3.61 (3H, OCH,) and a pair of doublets ( J = 7 and 1.5 c.p.5.) centered a t 1.86 (3H, CCH3). A solution of 16.0 g. (48 mmoles) of the phosphorane 1 and 4.7 g. (106 mmoles) of acetaldehyde in 250 ml. of methanol was stirred overnight a t room temperature and then diluted with water and extracted with ether. The ethereal extract was dried, concentrated, and distilled to separate 7 g . of material, b.p. 6092", containing16 both esters 2 and 3 as well as methanol and ether. After this distillate had been partitioned between pentane and aqueous sodium chloride, distillation of the pentane layer separated 1.8 g. (387,) of a mixture of esters, b.p. 90-115", containing'7 28% of the cis isomer 3 (first eluted) and 72y0 of the trans isomer 2 (second eluted). Collected samples of both isomers were identified with authentic samples by comparison of N

(19) Determined as a solution in 95% ethanol. (20) L. Horner and A. Mentrup, Ann., 646, 65 (1961). (21) D. E. McGreer, J . 0 7 8 . Chem., 16, 852 (1960). (22) K . von Auwers and F. Konia, Ann., 496, 252 (1932). (23) A column packed with 4-methyl-4-nitropimelonitrile suspended on Chromosorb P was employed. (24) Comparable spectroscopic properties have been reported previously by R . R. Fraser and D. E. McGreer, Can. J . Chem., 89, 505 (1961).

KOVEMBER, 1964

WITTIGREACTION WITH STABILIZED YLIDS

their infrared, mass, and n.m.r. spectra. For the quantitative experiments, summarized in Table 11, acetaldehyde was added to a solution of the phosphorane 1 and the resulting solution was stirred a t room temperature for 30 min. When no salt was present in the reaction mixture, ethylbenzene (an internal standard) was added and the solution was analyzed16directly. When an added salt was present, the solution was poured into water and extracted repeatedly with methylene chloride. After the resulting methylene chloride solution had been dried, the internal standard (ethylbenzene) was added and the solution was analyzed.16 As a control experiment to demonstrate lack of equilibration or unintentional fractionation of the esters 2 and 3 , a mixture of 16.4 mg. (0.16 mmole) of the cis ester 3, 158 mg. (0.47 mole) of the phosphorane and 380 mg. (8.7 moles) of acetaldehyde in 1 ml. of dimethylformamide was stirred a t room temperature for 18 hr. Analysis of the reaction mixture indicated the presence of 71% of the trans ester 2 and 29% of the cis ester corresponding to the calculated values if no equilibration or fractionation occurred. Comparable experiments in methanol solution and in dimethylformamide solution with lithium bromide present demonstrated the lack of significant fractionation or isomerization under these conditions. A solution containing 1.0 mmole of the phosphorane 1 and 4.3 mmoles of acetaldehyde in 4 ml. of chloroform was stirred a t 0". Aliquots (20 pl.) were removed and quenched in 80 r l . of chloroform a t measured time intervals, and the infrared spectra were measured in the 150c-1800-cm. -l region to follow the formation of the ester mixture (at 1650 em.-') and the consumption of the phosphorane 1 (at 1620 em.-'). The reaction was essentially complete in 9 min. under these conditions and the rates of disappearance of the phosphorane and of formation of the ester were approximately equal in agreement with the previous conclusion, based on kinetic that a betaine intermediate does not accumulate in the reaction mixture. Reaction of the Phosphonate Anion 10 with Acetaldehyde.-A mixture of 243.4 mg. (10 mmoles) of sodium hydride and 7.127 g. (10 mmoles) of methyl diethylphosphonoacetate in 10 ml. of 1,2-dimethoxyethane was stirred for 30 min. a t which time 205 ml. (81% of the theoretical amount) of hydrogen had been evolved. The resulting solution was treated with 4.0 g. (90 mrnoles) of acetaldehyde which resulted in the immediate separation of a solid. The reaction mixture was stirred for 30 min. a t room temperature and then poured into water and extracted with ether. The ethereal solution, after drying and concentration, contained16 4% of the cis ester 3 and 96% of the trans ester 2 . The products were identified with authentic samples by comparison of retention times and by comparison of the infrared spectra of collected samples. From a comparable reaction the precipitate which formed upon addition of acetaldehyde was separated and dissolved in water. An ether extract of this solution contained only trace amounts of the trans ester 2 indicating that this precipitate was sodium diethylphosphate. From an analogous reaction employing 1.2031 g. (5.7 mmoles) of methyl diethylphosphonoacetate, 141.7 mg. (5.9 mmoles) of sodium hydride, and 780 mg. (17.6 mmoles) of acetaldehyde in 12 ml. of dimethylformamide, the crude product was mixed with 332.7 mg. of ethylbenzene (an iAterna1 standard) and analyzed.16 The calculated yield of crotonic esters was 757, composed of 5y0 of the cis ester 3 and 95% of the trans ester 2 . A similar procedure with a solution of 482 mg. (2.3 mmoles) of the phosphonate, 52.6 mg. (2.2 mmoles) of sodium hydride, 150 mg. (1.7 mmoles) of lithium bromide, and 390 mg. (9.0 mmoles) of acetaldehyde in 6 ml. of dimethylformamide yielded 85uh of the ester mixture containing 7% of the cis isomer 3 and 9370 of the trans isomer 2. A control experiment of the type previously described demonstrated the absence of significant isomerization or fractionation of the isomeric esters by the reaction conditions or the analytical procedure. Reaction of the Ylid 1 with Chloroaceta1dehyde.-Reaction of either the dimethyl acetal or the diethyl acetal of chloroacetaldehyde with oxalic acid as previously describedz6produced crude chloroacetaldehyde, b.p. 88-93', which. was converted26 to its trimer and isolated as white needles from ethanol, m.p. 85-87" (lit.2s87.5'). The trimer has no absorption17 in the 6-p region of the infrared attributable to a carbonyl function and exhibits n.m.r. peaks" a t 6 5.30 (3H, triplet with J = 5 c.p.s., -0CHO-) and a t 3.72 (6H, doublet with J = 5 c.p.s., CICHZ-). (25) P. J. D e Bievre, G. P. Van der Kelen. G . Cornille, and Z . Eckhaut. Bull. S O C . c h i m . Belues, 68, 550 (1959).

3331

Distillation of this trimer immediately before use yielded chloroacetaldehyde, b.p. 85-86' (lit.2586"), with infrared absorption17 a t 1730 cm.? (C=O). To a solution of 2.58 g. (33 mmoles) of chloroacetaldehyde in 25 ml. of methylene chloride was added, dropwise and with stirring over a period of 1 hr., a solution of 11.1 g. (33 mmoles) of the phosphorane 1 in 40 ml. of methylene chloride. After the resulting mixture had been refluxed for 2 hr. and allowed to stand overnight, it was concentrated and diluted with petroleum ether (b.p. 3C-60') to precipitate the bulk of the triphenylphosphine oxide (8.26 g. or 90%). The remaining solution was concentrated and distilled through a 30cm. Holtzmann column to separate 2.4872 g. (57%) of fractions, b.p. 72-78' (18-19 mm.), 1.4600-1.4630, containingz6 approximately 337, of the cis ester 8 (first eluted) and approximately 677, of the trans ester 7 (second eluted). Each of the pure isomers was collected from the chromatograph26 and redistilled for c h a r a c t e r i ~ a t i o n . ~The ~ cia isomer 8, b.p. 55" (12 mm.), nZ41)1.4590, has infrared absorption17 a t 1730 (C=O) and a t 1650 em.-' (C=C) with an ultraviolet maxirnumlg a t 207 mp (e 12,600) and n.m.r. absorption14attributable to the vinyl protons a t 6 6.12 ( I H , pair of overlapping triplets with J = 6 and 11 c.p.5.) and a t 5.67 ( l H , pair of triplets with J = 1 and 11 c.p.5.) as well as a pair of doublets ( J = 1 and 6 c.P.s.) centered a t 4.51 (2H, -CH&I) and a singlet a t 3.61 (3H, -OCH,). The trans isomer 7, b.p. 68.5" (11 mm.), n z 41.4650, ~ has infrared absorption17 a t 1730 (C=O), a t 1665 (C=C), and a t 975 cm.-l (trans CH=CH) with an ultraviolet maximum1g a t 206 mA (e 14,400). The sample has n.m.r. peaks14 attributable to vinyl protons a t 6 6.86 ( I H , pair of triplets with J = 6 and 15 c.p.s.1 and a t 5.89 (1" pair of triplets with J = 1 and 15 c.p.5.) as well as a pair of doublets ( J = 1 and 6 c.p.5.) centered a t 6 4.03 (2H, -CH2C1) and a singlet a t 3.63 (3H, -0CHa). '4nal. Calcd. for CsH7Cloz: C, 44.64; H, 5.25; C1, 26.23; mol. wt., 134 and 136. Found for the cis isomer: C, 44.74; H , 8.47; C1, 26.25; mol. wt., 134 and 136 (mass spectrum). Found for the trans isomer: C, 44.55; H, 5.22; C1, 26.06; mol. wt., 134 and 136 (mass spectrum). During separation of the chlorocrotonic esters 7 and 8, the cis isomer 8 was observed to be converted to crotonolactone (9) on gas chromatography columns a t high temperatures. Consequently an authentic sample of this lactone 9 was prepared to establish its absence in the subsequently described quantitative reaction studies. To a solution of 165 g. of an acetic acid solution containing 0.85 mole of peracetic acid in 350 ml. of ethyl acetate was added 15 g. of sodium acetate. To this mixture, kept a t 23", was added, dropwise and with stirring, 92.6 g. (0.81 mole) of ethyl 3-butenoate.28 The reaction mixture was stirred for 60 hr. a t 23-25" and then neutralized to pH 7.5 by the addition of aqueous sodium carbonate. After separation of the organic layer, the aqueous phase was extracted with ether. The combined organic solutions were dried, concentrated, and distilled to separate 28 g. of the starting ester, b.p. 2575" (18 mm.), n Z 51.4078, ~ and 60.22 g. (57.47,) of ethyl 3,4epoxybutyrate as a colorless liquid, b.p. 79" (18 mm.), n Z 5 ~ 1.4208.zg This epoxy ester has infrared absorption17 a t 1735 cm.+ (ester C=O) with no significant ultraviolet absorption (e 75 a t 210 mp)19 and exhibits a single peak on gas chromatography.m A mixture of 10 g. (77 mmoles) of ethyl 3,4-epoxybutyrate and 30 g. of 10% aqueous sulfuric acid was stirred for 2 hr. at 40-46' and then continuously extracted with ether for 36 hr. The organic extract was concentrated and distilled31 to separate 1.75 g. (27.3%) of crotonolactone (9) as a colorless liquid, b.p. 7173" (2.9 mm.), n Z 51.4659 ~ [lit.32b.p. 100-102" (18 mm.), n 2 5 ~ 1.46601, which contained30 less than 1%, of impurities. The (26) A column packed with 20 M Carbowax suspended on ground firebrick was employed. (27) R . Rambaud and M. Brini-Fritz (BUZZ. S O C . c h i m . France, 1426 (1958)I have reported methyl 7-chlorocrotonate (stereochemistry not specified) to be aliquid, b . p . 80-81- (19 m m . ) , n'PD 1.469. (28) This ester was kindly supplied b y Dr. D. L. Heywood, Union Carbide Chemicals Co. (29) R. Rambaud, S. Ducher. A . Broche. M. Brini-Fritz, and M. Vessiere [Bull. sac. c k i m . France, 877 (1955)l report b.p. 75.5-76' (16 tnm.), n ' j D 1.427. (30) A column packed with 1540 Carbowax suspended on ground firebrick was employed. (31) If the acid in the extract was neutralized prior t o distillation, the distillate was primarily 3-hydroxybutyrolactone; c/. ref. 29. (32) N . C. Kaas, F. Limborg, and K . Glens, A c t a C k e m . Scnnd., 6 , 531 (1952).

HOUSE,JONES, A N D FRANK

3332

REACTIOX OF Phosphorane 1. mmoles

ClCHiCHO,

mmoles

THE

TABLEI V PHOSPHORANE 1 WITH CHLOROACETALDEHYDE

Solvent

Additive (mmoles)

(ml.1

1.0 0.97 CHzCL ( 3 ) 1.35 0.95 MecH (3) 1.03 0.96 III\lFc(3) DhIFc( 3 ) 0.85 0.97 0.94 0.98 DhIFc(3) I>hIFc ( 3 ) 0.99 0.97 The range of yields obtained is indicated. Average values average value by less than *3%. Dimethylformamide.

REACTION OF

THE

Solvent (ml.1

Additive (mmoles)

0.69 to 1 . 6 1 . 0 to 1 . 1 1.3

C6H6 ( 3 to 5 ) DMFc (3 to 5) C&3(3) DMFc ( 5 ) MeOH (3) EtOH (3) C B H( ~8 )

... ...

0.71 0.79 1.14

+

...

... ...

Yield,

--Composition---

%

% cis 8

5%

trans 7

84-96' 29 71h 86-95a 52b 48 , . . 67-95a 17b 83 LiBr (0.90) 85 33 67 LiNO, (1.19) 91 34 66 LiC104 (0.95) 94 31 69 from two determinations. The individual values differed from the ... . . .

TABLE V YLID4 PREPARED USING7~-BUTYLLITHIUM WITH

Propionaldehyde, mmoles

1

VOL. 29

AN

EQUIMOLAR QUANTITY O F PROPIONALDEHYDE Yield,

--5%

Composition----

32-83' 32-44' 43

23* 44b 44

70trans 77b 56 56

37 46 65

52 50 25

48 50 75

7c

cis 6

6

LiBr (2.8) suspension 0.49 C&(7) LiBr (5.6) 68 26 74 suspension 1.4 C6He (6) LiBr (1.4) 77d 23 77 suspension 3.5 CeHa (17) LiI (7.1) e 25 75 suspension 0.80 DMFc (5) LiBr (1.6) 48 46 54 solution The range of yields obtained. * These are average values from two or more determinations. Individual values differed from these average values by k37, or less. c Dimethylformamide. d In this run the reaction mixture was stirred for 18 hr. a t room temperature and then refluxed for 2 hr. prior to analysis. e I n this run the reaction mixture was stirred overnight and then refluxed for 3 hr. prior to analysis. lactone 9 has infrared absorption at 1740 and 1775 cm.-' (C=O)33 with an ultraviolet maximum34a t 208 mp ( c 5140) and n.m.r. absorption corresponding to the published35 spectrum. The quantitative results, summarized in Table IV, were obtained by adding freshly distilled chloroacetaldehyde to solutions of the phosphorane 1 and added salts (if any). After the reaction mixtures had been stirred for 30 min., n-pentyl ether was added as an internal standard and solutions in methanol or methylene chloride were analyzed16 directly. Solutions in dimethylformamide were diluted with ether, washed with water, and dried prior to analysis. The products were identified with previously described samples by comparison of retention times and by comparison of the infrared and mass spectra of collected samples. The absence of crotonolactone (9) in the products eluted from the gas chromatograph18 was demonstrated both by collection of samples (which lacked infrared absorption characteristic of the lactone 9) and by comparison of retention times [on the column used, the lactone 9 was eluted after both the czs ester 8 (first eluted) and the trans ester 7 (second eluted)]. From a control experiment employing 11 mg. (0.08 mmole) of the cis ester 8 , 357.5 mg. (1.07 mmoles) of the phosphorane 1 and 74.1 mg. (0.94 mmole) of chloroacetaldehyde in 3 ml. of dimethylformamide, the resulting ester mixture contained'e 22Yc of the czs ester 8 and 78% of the trans ester 7. The calculated values in the absence of equilibratlon are 24 and 757,, respectively. Reaction of the Ylid 11 with Chloroaceta1dehyde.-A solution of 10.2 g. (25 mmoles) of the phosphorane 11 and 1.997 g. (25 mmoles) of freshly distilled chloroacetaldehyde in 120 ml. of methylene chloride was refluxed for 2 hr., allowed to stand overnight, and then ronrentrated. After the residual solid had (33) The carbonyl doublet in these lactones is thought to arise from Fermi resonance: see R. N. Jones, C , L. Angell, T. Ito. and R. J. D. Smith. Can. J . Chern., 37,2007 (1959). (34) Determined in isooctane solution. (35) "N.M.R. Spectra Catalog." Varian Associates, Palo Alto, Calif. 1962,Spectrum No. 51.

been continuously extracted with pentane for 120 hr., concentration of the pentane extract separated 3.14 g. (64.4"7,) of the crude, crystalline, unsaturated ketone 12, m.p. 35-40'. Sublimation (25' a t 0.02 mm.) of this material afforded the pure ketone 12 as white prisms, m.p. 39.5-40.5", with infrared absorptionI2 a t 1690 and 1670 cm.-' (conjugate C=O), a t 1630 (conjugate C=C) and a t 977 ern.? (trans CH=CH) as well as an ultraviolet maximum36 a t 212 m r (e 1800). The sample has broad n.m.r. absorptionI4a t 6 7.39 (5H, aryl C-H) with a singlet a t 3.90 (2H, ArCH2CO), a doublet ( J = 5.5 c.p.5.) a t 4.19 (2H, CICHZ-), and absorption attributable to the vinyl protons a t 6.48 (lH, doublet with J = 16 c.P.s., long-range coupling perceptible but not resolved) and a t 6 6.97 ( l H , pair of triplets with J = 5.5 and 16 c.p.s.). ilnal. Calcd. for CIIH~ICIO:C, 67.87; H, 5.70; C1, 18.22; mol. wt., 194 and 196. Found: C, 68.00; H, 5.94; CI, 18.14; mol. wt., 194 and 196 (mass spectrum). Various efforts to isolate or confirm the presence of the cischloro ketone analogous to 12 in the reaction mixtures wsre unsuccessful. We are therefore uncertain of the degree of stereoselectivity in this reaction. Reaction of the Ylid 4 with Propionaldehyde.-A stirred suspension of 4.34 g. (11.1 mmoles) of benzyltriphenylphosphonium chloride in 20 ml. of benzene was treated with 5.5 ml. of a hexane solution37 containing 11 mmoles of n-butyllithium whereupon the red-orange color characteristic of the ylid 4 developed immediately. After the resulting suspension had been stirred for 15 min. a t room temperature, propionaldehyde (480 mg. or 8.3 mmoles) was added until the red color was discharged. The reaction mixture was stirred for 30 min. and then filtered. The filtrate was washed with water, dried, concentrated, and distilled to separate 600 mg. (547,) of a mixture of olefins, b.p. 60-62' (5 nim.) [lit.3bb.p. 84-85' (23 mm.) forcisisomer 6 (36) Determined as a solution in n-heptane. (37) The hexane solution of n-butyllithium was purchased from Foote Mineral Co., New Johnsonville, Tenn.

NOVEMBER, 1964

Two- AKD THREE-ATOM BRIDGED BIPHENYLS

and 91-92" (23 mm.) for trans isomer 51 containing16 257, of the cas olefin 6 (first eluted) and 757, of the trans olefin 5 (second eluted). Samples of each of the pure olefins 5 and 6 were collected from the chromatograph; the mass spectra of both products exhibit a molecular ion peak a t m/e = 132. The trans isomer 5 , n 2 51.5384 ~ (lit.s8n Z 61.5387), ~ has infrared absorption17 a t 1645 (C=C) and at 965 cm.-l (trans CH=CH) with an ultraviolet maximumlg at 254 mp (e 19,000) and an n.rn.r.l7 triplet ( J = 7 c.P.s.) a t 6 1.07 (3H, CH,) with a complex multiplet centered a t 2.17 (2H, CH,), a multiplet in the region 7.0 -7.3 (5H, aryl C-H), and a partially resolved multiplet centered a t 6.18 (2H, vinyl C-H).39 The cis isomer 6 has infrared absorption" a t 1635 (C=C) but lacks absorption in the region 95G1000 cm.-l. The material has an ultraviolet maximurnlg a t 242 mp (e 13,800) with an n.m.r.17 triplet ( J = 7 c.p.5.) a t 6 1.03 (3H, CH,), a multiplet centered a t 2.28 (2H, CH2),a partially resolved multiplet a t 7.12 (5H, aryl C-H), a doublet of triplets ( J = 11 and ca. 2 c.p.s.) centered a t 6.28 ( l H , vinyl C-H), and a doublet of triplets ( J = 11 and 7 c.p.5.) centered a t 5.52 ( I H , vinyl C-H). For the quantitative experiments; summarized in Table V, stock solutions of the ylid 4 in benzene were prepared using n-butyllithium in hexane as previously described. Negative Gilman color tests established the absence of n-butyllithium in these solutions. The insoluble materials were allowed to settle and aliquots of the clear, supernatant liquid were employed. For reactions in solvents other than benzene, the solvent was removed from an aliquot of the benzene solution under nitrogen and the residual red-orange solid was redissolved in the desired solvent. Titrations of aliquots of various ylid preparations with propionaldehyde indicated that the ylid concentration in the benzene solutions ranged from 0.16 to 0.43 M . Titration of aqueous extracts of various aliquots for chloride ion indicated that the chloride ion concentration in solution was in the range 0.11 to 0.15 M . For the experiments listed in Table V solutions (38) C. G. Overberger and I). Tanner, J . A m . Chem. Soc.,7 7 , 369 (1955). (39) Except for the expected differences in multiplicity, the n.m.r. peaks for the vinyl protons in the 1-phenyl-I-butenes resemble closely the spectra of the corresponding 1-phenyl-1-propenes: see ( a ) J. A . Pople, W , G. Schneider, and H . J. Bernstein, "High-Resolution Nuclear Magnetic Resonance," McGraw-Hill Book Co., Inc., New York, N. Y., 1959, pp. 238-240; (b) M. J. S.Dewar and R . C. Fahey, J . A m . Chem. Soc.,85, 3645 (1963).

3333

of the ylid in the specified solvent and containing any specified additives were titrated with propionaldehyde until the red color of the ylid was just discharged. In cases where ethanol or methanol was used as the solvent, the red color of the ylid was discharged upon addition of the solvent. Consequently, the amount of propionaldehyde added in these cases was determined from a knowledge of the ylid concentration in the original benzene solution. Unless otherwise noted the reaction mixtures were stirred a t room temperature for 30 min. and then a weighed amount of tetralin (as an internal standard) was added and the solutions were washed with water, dried, and analyzed.I6 Fine suspensions of lithium bromide in benzene-hexane mixtures were prepared by passing dry hydrogen bromide into a solution containing 35 mmoles of n-butyllithium in a mixture of 15 ml. of hexane and 10 ml. of benzene until a negative Gilman color test for n-butyllithium was obtained.4o Any excess hydrogen bromide was allowed to escape. Addition of this suspension to solutions of the ylid 4 in either benzene or dimethylformamide solution did not discharge the red color of the ylid, provided that no hydrogen bromide was present. Solutions of the ylid 4 were also generated by reaction of benzyltriphenylphosphonium chloride with sodium ethoxide in either ethanol or dimethylformamide. The reaction mixtures were stirred at room temperature for the specified times and then worked up and analyzed as previously described. The results are summarized in Table VI.

TABLE VI REACTION O F THE YLID 4 P R E P A R E D 1;SING SODIUM WITH AN EQUIMOLAR QUANTITY ETHOXIDE OF

Propionaldehyde, mmoles

Solvent (ml.)

1.81 4.6

DMFa (10)

PROPIONALDEHYDE

EtOH (6)

0.5 DMFa(4) Dimethylformamide.

Reaction time, hr.

Yield,

1 2 12 2

95 42 66 57

%

-Composition-% cia 6 % trans 5

46 46 46 45

54 54 54 55

a

(40) This is apparently the same procedure previously described: ref. 4.

see

Transformation Products of the Photoadduct of p-Xylene and Phenanthrenequinone. Some Two- and Three-Atom Bridged Biphenyls' ~ I O R D E CB.ARUBIX I Department of Chemistry, Carnegie Institute of Technology, Pittsburgh 13, Pennsylvania Received M a y 21, 1964 The photoadduct of p-xylene and phenanthrenequinone, 9,10-dihydro-9-hydroxy-9-(p-methylbenzyl)-lOketophenanthrene ( 1), has been synthesized by osmium tetroxide hydroxylation of 9-(p-methylbenzy1)phenanthrene to cis-9,10-dihydro-9,10-dihydroxy-9-p-methylbenzylphenanthrene ( 5 ) followed by oxidation. Sodium borohydride reduction of 1 afforded the trans isomer (3a) of 5 , cleaved by periodate to 2'-p-methylphenylacetyl)biphenyl-2-carboxaldehyde ( 6 ) which underwent facile intramolecular aldol condensation on Florisil to give ciscycloheptan-5-one (8 and 7). Both of these isomers were readily deand trans-5-p-tolyl-7-hydroxydibenzo[a,c] hydrated t o 6-(p-tolyl)-BH-dibenzo[a,c]cychhepten-5-c1ne (9). Catalytic hydrogenation of 9 yielded a mixture of 6-(p-tolyl)dibenzo[a,c]cycloheptan-5-one (IO) and cis-5-hydroxy-6-(p-tolyl)dibenzo[a,c]cycloheptane(1 1). Dehydration of 11 to 6-(p-tolyl)-5H-dibenzo [a,c]cycloheptene ( 12 ) followed by hydroboration furnished the trans isomer (13)of 11. The configurations assigned t o 7 and 8 were based on the Karplus relationship between dihedral angle and coupling constant of vicinal protons. The presence of a skewed conformation in dibenzo[a,c]cycloheptanes was suggested to account for the anomalous coupling constants observed with 11 and 13.

The revised structure 1 has recently been assigned2to the adduct formed by irradiation of solutions of 9,lOphenanthrenequinone in p-xylene3 with ultraviolet light. This report presents the results of chemical transformations of 1 which have provided further evi(1) Presented in part a t the 147th National Meeting of the American Chemical Society, Philadelphia, Pa., April, 1964. (2) M . B. Rubin and P. Zwitkowits, J . Ore. Chem., 29, 2362 (1964).

dence confirming the revised structure and have yielded a series of biphenyl derivatives which are of interest in themselves. '(3) ildducts of similar structure were obtained with toluene, o-, and mxylene among others. The p-xylene adduct was used in this work since the p-methyl substituent provided a convenient reference point for interpretation of n.m.r. spectra while not influencing the course of reaction a t remote positions.