SOVEMBER, 1964
REACTIONS OF BORONOPHTHALIDE
with trimethylamine than does B(HC=CH2)3 or B(CH2-CH3),. The stronger withdrawing ability of the CFC group compared with the -CH2CH3 group is usually attributed to the fact that the carbon atoms in the C=C group possess an sp configuration with more s character than the sp3 configuration of the carbon atonis in the -CH2CH3 group. I n coniparing the acidities of trihexynyl- and triphenylethynylborane, one might consider only the effect of the butyl and phenyl groups in altering the electronwithdrawing capability of the C=C group. The butyl group is clearly electron donating and such an effect would tend to reduce the acidity of the boron atom and decrease the stability of an amine complex of that compound. A phenyl group adjacent to the C-C group, would be niuch less electron donating than a butyl group and furthermore could act as an electron sink for *-electron delocalization. Such an effect would increase the acidity of the boron atom and hence increase the stability of an amine complex of that borane. The infrared spectra of the alkynylborane-amine complexes show that the absorption band of the carbon-carbon triple bond is shifted to a lower frequency (4.86 p ) than is recorded for acetylenic hydrocarbons (4.67 p ) . Such an effect indicates some mobility of the n-electrons of the C=C group to produce some carbon-carbon double bond character. The amine portion of the alkynylborane-amine coniplexes can be replaced by treating the amine com-
3229
plex with another amine base. Triethynylborane diethylamine can be prepared readily in essentially quantitative yield by refluxing triethynylborane-pyridine in diethylamine. The triethynylborane-amine coniplexes (HC=C)aB .pyridine
+ (CZHK)ZNH
--f
+
( H C = C ) g B . N ( C 2 H 5 ) ~ H pyridine
(9)
of diethylamine and trimethylamine were formed in good yield by this method and were found to be stable to the atmosphere. Attempts to prepare the animonia and hydrazine complexes by transamination resulted in the isolation of mushy solids that were very air sensitive. Unfortunately, analyses of the latter two complexes were not consistent and hence the true identities of the product were not established. In summary, all attempts to prepare triethynylborane or trihexynylborane by the reaction of the appropriate sodium acetylide with a boron halide resulted in what appeared to be polymerization of the products. Success was attained, however, in the preparation of stable amine complexes of triethynylborane and tri(phenylethyny1)borane by reaction of the appropriate alkynylsodium compound with boron halide-amine compounds. Alkynylborane-amine compounds were also prepared by transamination of triethynylboranepyridine with the desired amine. The alkynylboraneanlines are stable to the atmosphere and to shock. -
Arylboronic Acids.
VIII. Reactions of Boronophthalide'
R. R. H A Y N E SA N~D H. R. SNYDER Noyes Chemzcal Laboratory, University of Illinois, Urbana, I l l i m i s Received April 7, 1964 The ethyl, cyclohexyl, and benzyl esters of boronophthalide ( I a ) were prepared. Boronophthalide anhydride was prepared by the reduced pressure distillation of the molten phthalide. The reaction of boronophthalide, boronophthalide anhydride, or the ethyl ester of boronophthalide with phosphorus pentachloride yielded Bchloroboronophthalide and o-chloromethylbenzeneboronic anhydride. The reaction of the cyclohexyl ester of boronophthalide with dicyclohexyl chloroboronate yielded only B-chloroboronphthalide. The reaction of boronophthalide with excws phenyl- and o-tolylmagnesium halide yielded the B-aryl derivatives, while reaction with methyl- and ethylmagnesium halide yielded the B-alkyl derivatives and B-(o-hydroxymethylphenyl)boronophthalide.
In comparison with most simple esters of boronic acids the cyclic ester Ia, which has been called boronophthalide, is remarkably resistant to hydrolysis of the link between the alkoxy1 group and the boron a t o m 3 The carbon-boron link of the substance is also much more stable to hydrolytic cleavage than that in the similarly constituted arylboronic acids, e.g., o-tolueneboronic acids4 I t is thus of interest to prepare derivatives of Ia in which the hydroxyl group is replaced by other functions and to examine the effects of such replacenients on the stability of the lactone ring. The ethanolamine ester of boronophthalide (Ib) has been prepared5; it is quite stable toward hydrolysis, (1) P a r t of this work was supported by a grant from the Atomic Energy Commission: Report No. COO-314-10. (2) Standard Oil of California Fellow, 1980-1961; Allied Chemical Corporation Fellow, 1981-1962. (3) H. R . Snyder, A. J. Reedy. and W. J. Lennarz, J. A m . Chem. Soc.. 80, 835 (1958); W. J. Lennarz and H. R . Snyder, ibid., 84, 2172 (1960). (4) M. F. Lappert. Chem. Rev., 66, 959 (1956). ( 5 ) R . K. Kurz, P1i.D. Thesis, University of Illinois, 1961.
but much of its stability results from the coordination between the amino group and the boron atom. The presence of the amino group makes this ester unsuitable in tests with many reagents, e.g., phosphorus pentachloride. The simple alkyl esters (IC-e) which have now
Ia, R = H b , R = CH2CHZNHZ C, R = C2Hs d, R CH2CsHs e, R = CsH,,
I1
been prepared are extremely sensitive to hydrolysis a t the acyclic boron-xygen linkage. They rapidly absorb moisture from the air and revert to boronophthalide. However, with suitable precautions they can be used as intermediates. The anhydride (11)also reverts to boro-
3230
HAYNESAND SNYDER
nophthalide upon exposure to the moisture of the air. The anhydride is easily prepared by distilling the molten boronophthalide under reduced pressure (b.p. 136O at 0.4 mm.) ; earlier attempts to prepare it under milder conditions or by the action of thionyl chloride on boronoph thalide were unsuccessful. 3 Esters and anhydrides of boronic and borinic acids have been shown to react with phosphorus pentachloride to give the chlorides of the boronic and borinic acids.6-8 When the anhydride (11) was treated with phosphorus pentachloride, B-chloroboronophthalide (IIIa) was obtained in moderate yield (34%) along with an equivalent amount of o-chloromethylbenzeneboronic anhydride (IV). Under the same conditions, the ethyl ester of
VOL.29
*
34 1.5% and 33 f 3%, respectively. The ratio of products suggests a mechanism analogous to the one outlined above for the reaction of phosphorus pentachloride and a dialkyl arylboronate, as shown in eq. 2. PClS
f
IIIa
+ IV + POC1,
(2)
It should be noted that, if coordination occurred ini-13
IIIa, R = C1 b, R = C E H ~ C, R = o - C H ~ C E H ~ d , R = CHI e, R = CzHa
IV
boronophthalide yielded 42% of the B-chloro compound (IIIa) and 31% of the chloromethyl anhydride (IV). Boronophthalide itself gave little (8.5%) of the Bchloro compound (IIIa) and much (65%) of the chloromethyl anhydride (IV). Hydrolysis of either chloro compound (IIIa or IV) led to the formation of boronophthalide. No mechanism has been postulated for the reaction of phosphorus pentachloride with anhydrides or esters of boron compounds. However, a reasonable first step in such a reaction is the coordination of the halide with an oxygen atom in the boron compound. The resulting weakened B-0 bond may then undergo cleavage to form the products as shown in eq. 1. Whereas the Ar-B,
/OR OR 4
ClPCl*
-
/OR ArB ‘CI
+
/ \
R q,PCL
CI
L RCl + POCh
(I)
oxygen atoms are equivalent in the esters and trimeric anhydrides of boronic acids, the oxygen atoms within boronophthalide or its esters and anhydride are nonequivalent and therefore would possess different degrees of ability to coordinate with phosphorus pentachloride. The oxygen atoms in the cyclic portions of boronophthalide anhydride have a greater electron density than the oxygen atom between the two boron atoms. Thus, in reaction with 1 mole of phosphorus pentachloride, coordination should occur at either of the oxygen atoms in the cyclic portion of the molecule. Therefore, by analogy to the reaction of boronates or anhydrides with phosphorus pentachloride, boronophthalide anhydride should yield B-chloroboronophthalide and o-chloromethylbenzeneboronic anhydride in a 1 : 1 ratio. When the reaction was carried out over periods of 3-12 hr., the yields of the two products were (6) D R Nielsen and W E McEwen, J A m Chem S O C ,79, 3081 (1957) (7) B M Mikhailovand N S Fedstov,Im Akad N a u k S S S R , Old Kham Yauk 375 (1956) (8) B M Mikhailov abzd , 376 (1956).
tially at the oxygen atom between the two boron atoms, only B-chloroboronophthalide would be formed. In the reaction of the ethyl ester of boronophthalide, the phosphorus pentachloride could coordinate initially with either oxygen. Coordination a t the ethoxyl oxygen would lead to the formation of B-chloroboronophthalide, while coordination at the oxygen in the cyclic system would yield the isomeric o-chloromethylbenzeneboronic anhydride. The yields of the two compounds (Bchloroboronophthalide, 42%, and o-chloromethylbenzeneboronic anhydride, 31.5%) indicate that of the two oxygen atoms in the ester, the one in the ethoxyl group is somewhat more nucleophilic and hence better able to initially coordinate with the pentachloride. Although boronic and .borinic acids themselves apparently have not been converted directly to the B-C1 derivatives by the action of phosphorus pentachloride, it would not be surprising if the conversion of boronophthalide to its chloride (IIIa) could be effected with this reagent. Boronophthalide is a weak nonprotic acid,g the hydroxyl group of which reacts with phenyl isocyanate in the same manner as an alcoholic hydroxyl group.5 If the hydroxyl group should react with phosphorous pentachloride in the same way as the alcoholic hydroxyl group reacts with this reagent,‘O forming the mixed anhydride VIa at the stage where the alcohol forms the ester ROPCl,, the expected product would be the B-C1 compound IIIa. However, if the attack of phosphorus pentachloride occurs preferentially at the ester oxygen atom of boronophthalide via V, then ring opening and subsequent steps would lead to the chloromethyl anhydride IV. The latter path evidently is greatly favored, for, when the reaction was carried out,
V
VI
Va
Via
(9) M. J. S. Dewar and R. C. Dougherty, J. Am. Chem. Soc., 84, 2648 (1962). (10) H. L. Goering and F. H. MoCarron, ibid., 78, 2270 (1956).
NOVEMBER, 1964
REACTIONS O F BORONOPHTHALIDE
o-chloromethylbenzeneboronic anhydride was isolated in 65.5% yield and B-chloroboronophthalide in only 8.3y0 yield. The possibility that the small amount of the B-C1 compound formed arises as a result of the conversion of boronophthalide to its anhydride and reaction of the latter discussed above, rather than by the more direct path through V and Va, cannot be entirely excluded; however, the stability of boronophthalide toward thionyl chloride argues against the formation of the anhydride by reaction with phosphorus pentachloride. Alkoxy1 groups of esters of boronic and borinic acids can be replaced by chlorine atoms in an exchange reaction with mixed ester-chlorides derived from boric acid.“ This process would appear to offer a route to
HzC-4
IIIa without the simultaneous formation of the chloromethyl anhydride (IV). The cyclohexyl esters shown in eq. 5 were chosen because all of them boil higher than B-chloroboronophthalide (IIIa),permitting control of the reaction by distillation of the desired product from the mixture. By this method B-chloroboronophthalide was obtained in 67% yield. A characteristic reaction of mixed ester-chlorides of aromatic boronic acids, ArB(OR)Cl, is their ready cleavage under the influence of catalytic amounts of Lewis acids to give the alkyl chlorides and the anhydrides of the aromatic boronic acids.’* Occurrence of this reaction would convert B-chloroboronophthalide to ochloromethylbenzeneboronic anhydride (IV). No indication of such conversion could be found in a test conducted with aluminum chloride in carbon disulfide for several hours at room temperature. It might be expected that a derivative of boronophthalide having an alkyl or aryl group in the place of the hydroxyl group could be prepared by the reaction of a Grignard reagent on boronophthalide or its anhydride, chloride, or esters. The possible reaction with boronophthalide itself is the most interesting, for the similar replacement of hydroxyl has been reported13 to occur with lO-hydroxy-l0,9-borazarophenanthrene(VII) but not with boroxaroisoquinoline9 (VIII), the structure of which is the more similar to that of boronophthalide. It has been suggested that the failure of the reaction in the second instance is due to the lesser degree of aromatic character in this system. Accordingly, it was somewhat surprising to find that the reaction of boronophthalide with aryl Grignard reagents gives excellent yields (70-80a/,) of B-aryl derivatives; the similar reaction occurs with alkyl Grignard reagents, but the yields of products isolated have been lower (30-5070). In the reaction with an alkylniagnesium halide two additional products were isolated ; they are benzyl alcohol and B(0-hydroxymethylphenyl) boronophthalide (IX) . (11) E. W . Abel, W. Gerrard, and M. F. Lappert, J. Chem. Soc., 3833 (1957). ( 1 2 ) P. B. Brindley, W. Gerrard, and M. F. Lappert, ibid., 1540 (1956). (13) M. J. S. Dewar, R. Diets. V. P. Kubba, and A. R . Lepley. J. A m . Chem. Soc., 83, 1754 (1961).
3231
BOH
OH VI1
IX
VI11
The simplest explanation for the formation of I X is that it arises by di~proportionation’~~ of a mixed alkylaryl borine (ArBR2). Such compounds are known to change rapidly to mixtures of the symmetrical borines, Ar3Band RaB. On the other hand, esters of alkyl-aryl borinic acids (ArB(R)OR) are stable; in the present work there was no indication that the B-alkylboronophthalides, once isolated, underwent disproportionation. In any scheme for the formation of I X froin a borine, an oxidative step is required for the replacenient of an aryl or alkyl residue by the oxygen function; such an oxidation might have occurred through contact with the air during work-up of the reaction mixtures. The benzyl alcohol isolated may have resulted from hydrolytic deboronation of one of the species present. Although the details of the reactions leading to I X are uncertain, it is probable that the reaction of boronophthalide with aliphatic Grignard reagents is accompanied by opening of the phthalide ring and the formation of borines.’4b The n.m.r. spectrum of I X showed only one peak in the methylene region, even at slow sweep. The hydrogen atom undoubtedly exchanges between the two oxygen atoms very rapidly, causing the two methylene groups to become equivalent. As expected, the spectrum of the a-naphthylurethane of I X shows two peaks of equal area (chemical shift difference = 15.8 c.P.s.) in the methylene region of the spectrum. A comparison of the ultraviolet spectra’s of boronophthalide and B-methylboronophthalide with those’6 of indane and indene (Table I) shows very close similarity between the boron compounds and the saturated hydrocarbon, suggesting very little pseudo-aromatic character in the heterocyclic rings of the boronophthalides. TABLE I ULTRAVIOLET SPECTRA OF INDANE, INDENE, BORONOPHTHALIDE, A N D B-METHYLBORONOPHTHALIDE Compd.
Indane (in hexane) Indene (in alcohol)
Boronophthalide (in alcohol) B-Methylboronophthalide (in alcohol)
hlax
log
274 267 260 291 286 279 249 275 268 263 278
3.25 3.16 3.00 2.37 2.40 2.65 4.06 3.05 3.03 2.85 3.04
f
271
3.01
264
2.85
(14) (a) K. Torssell, Acta Chem. Scand., 9, 242 (1955). (b) Since this paper was submitted, M. J . S. Dewar and R. C. Dougherty [Tetrahedron Letters, 16, 907 (1964) I have reported the disproportionation of arylboronic acids to arylborinic acids under t h e influence of strong bases. A referee has suggested t h a t I X may arise by an analogous disproportionation of t h e intermediate alkyl Grignard complex. W e concur in t h e suggestion t h a t the disproportionation m a y occur a t t h e stage of t h e Grignard complex. (15) Ultraviolet spectra were determined on a Bausch and L a m b Spectronic 550 spectrophotometer. (16) R . A. Morton and A. J. A. deGouveia, J . Chem. Soc., 913 (1934).
HAYNES AND SNYDER
3232
It is surprising that the spectra of boronophthalide and its B-methyl derivative are so nearly identical. The fact that only the ring oxygen is available to satisfy the electron demand of the boron atom in the latter compound would seem to require a greater contribution from forms like X in its structure than in that of boronophthalide itself. The spectra do not confirm this view.
+
x Experimental l7 Boronophtha1ide.-Boronophthalide was prepared by the method previously reported.3 Ethyl Ester of Boronophtha1ide.-Boronophthalide (3.3 g., 0.025 mole), ethanol (3.5 g., 0.077 mole), and 30 ml. of benzene were refluxed for 1 hr. A Dean-Stark tube was incorporated into the apparatus and the tertiary azeotrope of benzene-waterethanol was distilled from the reaction. The remaining ethanol and benzene were removed in vacuo and the resulting liquid was distilled under diminished pressure. The ester distilled a t 56-58" (0.8 mm.) and weighed 3.09 g. (77.37,). An analytical sample was obtained by twice distilling the ester ( n 2 6 ~1.4945). The infrared spectrum of the product shows absorption a t 1355 (B-0)la and 1000 cm.-l (boronolactone C-0) .I9 Anal. Calcd. for CgHIIBO1: C, 66.72; H, 6.84; B, 6.68. Found: C, 66.40; H , 6.84; B, 6.53. Benzyl Ester of Boronophtha1ide.-This ester was prepared in the same manner as the ethyl ester. The benzyl ester distilled a t 119-120" (0.5 mm.); 7 2 7 , yield; n Z 51.5654; ~ infrared spectrum, 1355 (B-0)18 and 1005 cm.? (C-O).19 Anal. Calcd. for C14H13B02: C, 75.08; H , 5.84; B, 4.83. Found: C, 75.31; H , 5.94; B , 4 . 7 1 . Cyclohexyl Ester of Boronophthalide .-This ester was prepared in the same manner as the ethyl ester. The cyclohexyl ester distilled a t 108-110" (0.5 mm.); 86.5Yc yield; 12% 1.5267; infrared spectrum, 1345 (B-O)l* and 998 cm.-l (C-O).19 Anal. Calcd. for C13H17B02: C, 72.25; H, 7.93; B, 5.01. Found: C, 72.31; H , 7.88; B, 4.92. Boronophthalide Anhydride.-Boronophthalide (10 g., 74.5 mmoles) was melted and then distilled under diminished pressure to give 8.4 g. (90.5y0) of the anhydride, b.p. 136-138' (0.4 mm.). The product readily solidified to a whitesolid, m.p. 62-64'. An analytical sample was obtained by redist,illation; infrared spectrum, 1355 (B-0)l8 and 995 cm.? (C-O).19 Anal. Calcd. for ClaH12B20,: C, 67.29; H , 4.84; B, 8.66. Found: C,67.14; H , 4 . 8 6 ; B,8.30. Hydrolysis of Boronophthalide Anhydride to Boronophthalide. -The anhydride (1 g., 4.0 mmoles) was dissolved in 25 ml. of boiling water. The solution was slowly allowed to cool to room temperature during which time a solid crystallized from solution. The white crystals were filtered and after air drying weighed 1.02 g. (95.5y0, m.p. 94-98"), After one recrystallization from water, a mixture melting point of the solid with a known sample of boronophthalide gave no depression. B-Chloroboronophthalide and o-Chloromethylbenzeneboronic Anhydride. From Boronophthalide and Phosphorus Pentachloride.-Boronophthalide (5 g., 37.2 mmoles) was dissolved in a mixture of 70 ml. of carbon tetrachloride and 20 ml. of ether and added slowly over a period of 2 hr. to a refluxing solution of 7.75 g. (37.2 mmoles) of phosphorus pentachloride in 50 ml. of carbon tetrachloride. After the addition was complete, the solution was (17) All melting points are uncorrected. Microanalyses and molecular weight determinations were performed b y MI. Josef Nemeth and associates. Infrared and nuclear magnetic resonance spectra were determined b y Mr. D. Johnson and associates using a Perkin-Elmer Model 21 infrared spectrophotometer (equipped with sodium chloride optics) and a Varian Associates Model A-60 nuclear magnetic resonance spectrometer. (18) L. J. Bellamy, W. Gerrard, M. F. Lappert, and R . L. Williams, J . Chem. Soc.. 2412 (1958). (19) H . R . Snyder and W. J. Lennarz. J . A m . Chem. Soc., 89, 2172 (1960).
VOL. 29
further refluxed for 2 hr. The solvents were removed in vacuo and the resulting semisolid mass was subjected to diminished pressure distillation with care to keep the pot temperature below 120'. After a forerun of phosphorus oxychloride, B-chloroboronophthalide distilled a t 56-58" (0.5 mm.). The substance readily solidified to give 0.47 g. (8.3%) of a white solid, m.p. 52-54'. An analytical sample was obtained by redistilling the compound; infrared spectrum, 1355 (B-O)**and 992 cm.-l (C-0)lo; n.m.r. spectrum,20aromatic T 2.00 (m) and 2.85 (m) and CH24.78 (s).21 Anal. Calcd. for C7H6BC10: C, 55.16; H , 3.96; B, 7.10. Found: C, .55.25; H,4.17; B, 7.37. The solid remaining in the distillation pot was dissolved in boiling carbon tetrachloride and the solution waa allowed to cool slowly to room temperature. The precipitated o-chloromethylbenzeneboronic anhydride was filtered and dried in vacuo; it weighed 3.7 g. (65.57,), m.p. 142-145". Two recrystallizations from carbon tetrachloride gave an analytical sample that melted at 145-146'; infrared spectrum, 1343 (B-0),18 no absorption in the region of C-0 (1OOG975 cm.-1).19 Anal. Calcd. for C7HeBC10: C, 55.16; H , 3.96; B, 7.10. Found: C, 55.31; H , 4.07; B , 6.75. From Boronophthalide Anhydride and Phosphorus Pentachloride.-Boronophthalide anhydride (6.9 g., 27.6 mmoles) was dissolved in 20 ml. of carbon tetrachloride and 5.75 g. (27.6 mmoles) of phosphorus pentachloride was added. The mixture was refluxed for 4 hr. and then the solvent was removed in vacuo. The resulting liquid was subjected to diminished pressure distillation. After a forerun of phosphorus oxychloride, B-chloroboronophthalide distilled a t 56-58' (0.5 mm.), 3.31-g. yield (36.2%). Work-up of the distillation residue as described above gave 3.1 g . (347,) of o-chloromethylbenzeneboronic anhydride. From the Ethyl Ester of Boronophthalide and Phosphorus Pentachloride.-The ethyl ester of boronophthalide (3.74 g., 23 mmoles) was dissolved in 10 ml. of carbon tetrachloride. Phosphorus pentachloride (4.9 g., 23 mmoles) was added and the mixture was refluxed for 3 hr. The solvent was removed in vacuo and the remaining liquid was distilled under diminished pressure. After a forerun of phosphorus oxychloride, B-chloroboronophthalide distilled a t 62-64" (0.6 mm.), 1.47-g. yield (42%). Work-up of the distillation residue as described above yielded 1.10 g. (31 5%)of o-chloromethylbenzeneboronic anhydride. From the Cyclohexyl Ester of Boronophthalide and Dicyclohexyl Ch1oroboronate.-The cyclohexyl ester of boronophthalide (13.5 g., 62.5 mmoles) was added dropwise to dicyclohexyl chloroboronate cooled to - 10". The chloroboronate was prepared from 12.5 g. (13.0 ml., 125 mmoles) of cyclohexyl alcohol and 7.32 g. (5.1 ml. a t O", 62.5 mmoles) of boron trichloride and reacted in situ. After addition of the ester, the reaction w&s allowed to warm to room temperature and stirred for 4 hr. The colorless liquid was then subjected to diminished pressure distillation. The B-chloroboronophthalide distilled a t 52-56' (0.5 mm.) over a period of 3 hr. The yield was 6.4 g. (67.5%). Work-up of the distillation residue as described above failed to yield any o-chloromethylbenzeneboronic anhydride. Hydrolysis of B-Chloroboronophtha1ide.-The B-chloro compound (0.11 g., 0.725 mmole) was treated with a mixture of 0.8 ml. of ether and 0.6 ml. of water. After the reaction was completed, the ether layer waa removed with a syringe and the aqueous layer was extracted with two 1-ml. portions of ether. The ether extracts were combined and placed on a watch glass. Evaporation of the ether gave 0.091 g. (93.8%) of a white solid, m.p. 92-96", After one recrystallization from water, the solid gave no depression in a mixture melting point determination with boronophthalide. Conversion of o-Chloromethylbenzeneboronic Anhydride to Boronophthalide .-o-Chloromethylbenzeneboronic anhydride (0.5 g., 1.61 mmoles) waa dissolved in 5 ml. of 10% sodium hydroxide. After standing for 1 hr., the solution was acidified with dilute hydrochloric acid to give a white precipitate. The solid was (20) Spectra were obtained in deuteriochloroform with tetramethylsilane as an internal standard. Chemical shifts are expressed as shielding values expressed in r-values as defined b y G . V. D. Tiers IJ. Phys. Chem., 2412 (1958)l. The abbreviations used in describing the peaks are as follows: s is singlet and m is an unresolved multiplet. With multiplet peaks, the mean value is reported. (21) It has been our experience that the methylene group of boronophthalide and its derivatives absorbs in the nuclear magnetic resonance spectrum in the general region from 7 4.6 to 5.0: cf. R . T . Hawkins, W. J . Lennarr. and H. R . Snyder, J. A m . Chem. S o c . , 83,3053 (1960).
YOVEMBER, 1964
REACTIONS O F BORONOPHTHALIDE
Bltered and air dried; it weighed 0.40 g. (92.8%). After one recrystallization from water, the product gave no depression in a mixture melting point determination with boronophthalide. Attempted Isomerization of B-Chloroboronophthalide with a Lewis Acid.-The chloro compound (1 g., 6.6 mmoles) was dissolved in 10 ml. of carbon disulfide. Anhydrous aluminum chloride (6 mg.) was added and the mixture was stirred a t room temperature for 5 hr. The solution was filtered and the solvent was removed in vacuo. The resulting liquid was distilled to give 0.67 g. (677, recovery) of B-chloroboronophthalide, identified by boiling point and comparison of its infrared spectrum with that of a known sample of B-chloroboronopht'halide. B-Phenylboronophtha1ide.-In a 500-ml. flask equipped with a mechanical stirrer, a nitrogen inlet tube, and a reflux condenser fitted with a calcium chloride tube was placed a solution of 9 g. (0.067 mole) of boronophthalide in 120 ml. of ether. Phenylmagnesium bromide, prepared from 5.5 g. (0.225 g.-atom) of magnesium and 35.2 g. (0.225 mole) of bromobenzene, was added dropwise to the ether solution of the boron compound over a period of 45 min. A white precipitate was formed immediately and continued to be formed until about one-half of the Grignard reagent had been added. The mixture was refluxed for l hr. and then stirred a t room temperature for 1 hr. It was then hydrolyzed with 60 ml. of 9.573 hydrochloric acid. The resulting ether layer was separated. The aqueous layer was extracted twice with two 30-ml. portions of ether and the ether solutions were combined and dried over magnesium sulfate. The ether was removed in vacuo and the resulting liquid was distilled under diminished pressure: fraction I , 75-80' (0.7 mm.); fraction 11, 108-112" (0.8 mm.). The first fraction weighed 0.72 g. and was shown to be biphenyl by mixture melting point with an authentic sample. Fraction I1 was the B-phenyl compound and weighed 9.27 g. (71.37,). An analytical sample was obtained by redistilling the liquid twice a t 98-99" (0.5 mm.); n Z 4 D1.6045; infrared spectrum, 1330 (B-0)18 and 985 om.-' (C-O)IQ; n.m.r. spectrum, aromatic T 1.95 (m) and 2.36 ( m ) and CHZ 4.74 ( 8 ) .zl A n a l . Calcd. for CL3H11BO: C, 80.46; H , 5.72; B, 5.58. Found: C, 80.18; H , 6.06; B, 5.35. Comparable yields were obtained when the boron compound was added to the Crignard reagent under the above-described reaction conditions, or if the ethyl ester of boronophthalide was used. B-o-Tolylboronophtha1ide.-This compound was prepared in the same manner as the B-phenyl derivative. The B-o-tolyl compound distilled a t 132-133' (0.5 mm.); 76.5% yield; 7 ~ 1.5708; infrared spectrum, 1323 (B-O)18 and 980 cm.? (C-O)lg; n.m.r. spectrum, aromatic T 2.00 ( m ) and 2.61 (m), CHZ4.62 (s),zl and CH3 7.37 ( 9 ) . A n d . Calcd. for C14H13BO: C, 80.75; H , 6.29; B, 5.19. Found: C, 80.24; H , 6.41; B,4.99. B-Methylboronophthalide and B-(o-Hydroxymethylpheny1)boronophthalide .-In a 300-ml. flask equipped with a mechanical stirrer, a nitrogen inlet tube, and a reflux condenser fitted with a calcium chloride drying tube was placed a solution of 5.0 g. (37.3 mmoles) of boronophthalide in60ml. of anhydrousether. Methylmagnesium iodide prepared from 2.72 g. (112 g.-atoms) of magnesium and 15.9 g. (7 ml., 112 mmoles) of methyl iodide was added dropwise to the ether solution of the boron compound over a period of 30 min. During the addition of the Grignard reagent, a fine precipitate formed which coagulated into a mass when about one-half of the Grignard reagent had been added. The mixture
3233
was refluxed for 1 hr. during which time the coagulated mass became dispersed. The mixture was stirred for an additional hour a t room temperature, then hydrolyzed with 60 ml. of 7.67, hydrochloric acid. The ether layer was separated and the aqueous layer was extracted with two 30-ml. portions of ether. The ether layers were combined and dried over magnesium sulfate. Removal of the ether zn vacuo yielded a mixture of a solid and a liquid. The solid was removed by filtration and the filtrate was distilled under diminished pressure: fraction I , b.p. 30-32' (0.9 mm.); fraction 11, b.p. 56-59' (0.9 mm.). The lower boiling substance (2.33 g., 47.5%) was B-methylboronophthalide. An analytical sample was obtained by further distillations ( n z s ~ 1.5398); infrared spectrum, 1345 (B-0)18 and 995 cm.? (C-O)lS; n.m.r. spectrum, aromatic T 2.25 (m) and 2.65 (m), CH2 4.85 ( s ) , ~and ~ CH39.22 (8). Anal. Calcd. for C*H,BO: C. 72.80:, H., 6.87: B. 8.20. Found: C, 73.16; H, 7:13-; B , 8.42. Fraction I1 (0.69 g., 177,) was benzyl alcohol. The alcohol was identified by converting it to its 1-naphthylurethane. A mixture melting point of the urethane with a known sample of the 1naphthylurethane of benzyl alcohol showed no depression. The solid removed by filtrationwas B-(0-hydroxymethylpheny1)boronophthalide (0.34 g., 8.157,). I t was purified by recrystallization from chloroform; m.p. 14.5146'; infrared spectrum, 3490 (OH), 1320 (B-O),18 and 980 cm.-l (C-O)l9; n.m.r. spectrum, aromatic T 2.68 (m), OH 4.48 (broad s), and CHZ5.02 (9). Anal. Calcd. for Cl4Hl3BO2: C, 75.08; H , 5.84; B, 4.83; mol. wt., 224. Found: C, 75.10; H , 6.04; B, 4.64; mol. wt. (Iiast method in camphor), 214. B-Ethylboronophthalide and B-(o-Hydroxymethylphenyl)boronophtha1ide.-This preparation was carried out in the same manner as the preceding reaction. B-Ethylboronophthalide distilled a t 43-44" (0.4 mm.); 28.4% yield; n z z . 61.5198; ~ infrared spectrum, 1347 (B-O)18 and 1015 cm.? (C-O)lQ; n.m.r. spectrum, aromatic T 2.22 (m) and 2.67 (m), CHI 4.64 (s),~~ and CZH5 8.75 (m) The benzyl alcohol (0.63 g., 8.7%) was identified as before. B-(o-Hydroxymethylpheny1)boronophthalidewas isolated in 137, yield. Reaction of B-(0-Hydroxymethylpheny1)boronophthalide with 1-Naphthyl Isocyanate.-To 288 mg. (1.28 mmoles) of B-(0-hydroxymethy1phenyl)boronophthalide dissolved in 20 ml. of refluxing chloroform was added 217 mg. (0.184 ml., 1.28 mmoles) of 1-naphthyl isocyanate. The solution was cooled slowly to 6 ~ temperature and then refrigerated. room The resulting solid was filtered free of the solvent, air dried, and weighed, yielding 0.457 g. (92.57,), m.p. 163-166'. An analytical sample was prepared by recrystallizing the urethane from a mixture of chloroform and high-boiling petroleum ether (b.p. 90-110°); m.p. 169-170"; infrared spectrum, 3280 (N-H), 1693 (C=O), 1318 (B-0),l8 and 980 cm.-' (C-0) . I Q A n a l . Calcd. for CZSHzUB03: C, 76.35; H , 5.13; B, 2.75; N , 3.66. Found: C,76.03; H,5.11; B,2.53; N,3.50. I
~
,
(22) That an ethyl group attached to a boron atom does not give the usual separated quartet-triplet in the nuclear magnetic resonance spectrum has been reported b y Stone. He studied the spectra of several ethylboron compounds, as well as their moleciilar addition compounds with bases, and found that there are only small differences in the chemical shifts of the methylene and methyl protons in the ethyl group. T. D. Coyle and F. G. A . Stone, J . A m . Chem. SOC.SS, 4138 (1961).
