2320 Stoichiometric concentration of n-BuaNC1 was used, without
allowance for incomplete dissociation. Product Analysis. Reaction mixtures were extracted with pentane, and the pentane layer was washed with water (in the case of 111 also with dilute acid and sodium bicarbonate) and dried over MgSOa; most of the solvent was evaporated and the remaining solution was analyzed by glc. Conditions were: for olefins IVVII, 25% Carbowax 4000 on Chromosorb W at 160-175"; for VI11 and IX, 6 z SE-30 on Chromosorb W at 30"; for X, 5 % Carbowax 4.000 on Chromosorb W at 67'. Samples of 1- and 3-phenyl~yclopentene,~~ of norbornene and nortricyclene,22and of exo- and endo-2-norbornyl chloride,23used (21) W. H. Tallent,J. Org. Chem., 21,862(1956).
for comparison, were available from earlier work. In some cases, absolute analysis of compounds VIII-IX and X was performed, using cyclohexane and decane, respectively, as internal standards, In all other cases relative amounts were determined. Relative areas were taken as the ratio of isomers in the case of olefins 1V and V. as well as of VI and VII.
Acknowledgment. We wish to thank Professor J. 0. Edwards for reading the manuscript. (22) E. A. Vogelfanger, Ph.D. Thesis, University of California, Los Angeles, 1963. (23) J. P. Hardy, Ph.D. Thesis, University of California, Los Angeles, 1967.
Allylic Oxidation of Olefins by Mercuric Acetate' Zvi Rappoport,*2 S. W i n ~ t e i n and , ~ W. G . Young
Contribution No. 2927 from the Department of Chemistry, University of California at Los Angeles, Los Angeles, California 90024. Received M a y 24, 1971 Both the oxidation of allylbenzene by Hg(OAc)? and the solvolysis of cinnamylmercuric acetate give 40x a-phenylallyl acetate and 60% cinnamyl acetate. The solvolysis of crotylmercuric acetate and the oxidations of 1-and 2-olefins C,H2,by Hg(OAc)2give under kinetic control exclusively the secondary allylic esters. The oxidation rate is apparently first order in the olefin-Hg(OAc)2 adduct. Rate-determining formation of the allylic HgOAc by an SE' reaction and consecutive product-determining solvolysis of the mercurial are suggested to be involved in the allylic oxidation. The allylic isomerizations of allylic mercurials and allylic acetates are discussed.
Abstract:
R
eaction of olefins with metal acetates M(OAc), the allylic mercuric acetates are usually the suggested (M = Hg11,4PdI1,j T1111,6PbIV)' gives a variety oxidation intermediates. Their formation by allylic of products including T complexes, adducts, diacetates, proton abstraction, followed by a radical decomposirearranged products, and allylic esters.8 The allylic tion, was initially suggested"" but the radical route product has been visualized to arise by elimination was later discarded.lob They may also be formed of HM(OAC),-~ from the olefin-metal acetate a d d ~ c t . ~ from the adduct by the loss of HOAc." Initial forHowever, in the allylic oxidation by mercuric acetate4~lc mation of an olefin-metal salt complex,12 which then gives rapidly the allylic mercurial, or electrophilic attack by HgOAc+ with simultaneous rearrangement (1) For preliminary communications see: (a) Z. Rappoport, P. D . Sleezer, S . Winstein and W. G. Young, Tetrahedron L e f f . ,3719 (1965); of the double bond,13 both followed by C-Hg bond (b) 2. Rappoport, L. I 9 0 x of 2 and 3, 2 x of 4 and traces of 5 . Table I gives the distribution of the allylic acetates PhCH=CHCHzHgOAc 1
2550 76.0 5.60
3450 87.5 6.00
14,100 100
Ca. 2 z of allylbenzene was observed. Hg was the only inorganic product.
of the allylic system are identical. However, when unsymmetrical olefins were oxidized, either the rearranged allylic ester" or at high temperature a mixture of both allylic ester^'^^'^ was obtained. Direct tests for the intermediacy of the organomercurials can be applied by studying their behavior under allylic oxidation conditions. Cinnamylmercuric acetate (1) is a possible intermediate in the Hg(OAc)* oxidation of allylbenzene (4) and propenylbenzene ( S ) , which gives a-phenylallyl acetate (2) and cinnamyl acetate (3).Ib Moreover, solvolysis of crotylmercuric acetate (6) gives >99.5 of a-methylallyl acetate (7) and 99% pure. 1-Octene (Matheson) was purified by distillation. Hg(OAc)* (Baker Analyzed) was crystallized from 2073 AcOH-80Z water and dried at 1IO" to constant weight. Acetic acid was prepared by fractionation from the calculated amount of acetic anhydride after reflux for 24 hr. The acid, bp 117" (753 mm), was dry to Karl Fischer reagent. 1,2-Diacetoxy-3-phenylpropane. 1,2-Dibromo-3-phenylpropane46(15 g) and silver acetate (20 g) were refluxed in acetic acid (150 ml) for 20.5 hr. The mixture was poured into water (500 ml) and extracted twice with methylene chloride (200 ml), the solvent was dried (Na2S04)and removed iii U ~ C I I Oand , the residue was distilled at 156" (8 mm), giving 12.6 g (98 %) of organic material containing 4 % cinnamyl acetate and ca. 95 % 1,2-diacetoxy-3~D nmr 6 phenylpropanen7which was purified by vpc: / z ~1.4900; 2.03 (6 H, 2 s, 2COMe), 2.98 ( 2 H, d, J = 7.2 Hz, benzyl), 4.23 (2 H, octet, terminal CH2), 5.41 (1 H, octet, CH), 7.50 (5 H, s, Ph). The octet splitting remains the same at 0 and 40". The ir IS very similar to that of cinnamyl acetate. Anal. Calcd for CI3H1&On: C, 66.08; H, 6.83 Found: C, 66.01; H , 6.56. Stabilities of Starting Materials and Products. Solutions of 0.27 M 7 and 0.61 M 8 in AcOH were kept for 13 days at 75". The recovered esters were >99% pure. 4 ( 1 M ) in AcOH was left for 97 hr at 75" with and without 1.48 M NaOAc. The recovered material was only 4, although 0.01% of 5 could be detected. Diethyl adipate (the vpc standard) was recovered unchanged from a 1 :2 mixture with Hg(0Ac)n at 75" for 1 week. 2 and 3 were stable on the XF-1150 column under the analysis conditions. 1,2-Diacetoxy-3-phenylpropane (189 mg) and Hg(OAc)2(725 mg) in AcOH (10 ml) were kept for 74 hr at 75". After work-up, >99.5% of the diacetate was recovered unchanged. Reactions of the Allylic Esters in the Presence of Hg(OAc)?. 7 (0.24 )Mand Hg(OAc)?(0.29 M ) were kept for 23 hr in acetic acid at 75". Only 38% of the allylic esters was recovered with a composition of 4 0 z 7 and 60% 8. When 0.2 M 7 and 0.2 M Hg(OAc)? in AcOH were kept for 5 hr at 50", the recovered ester was 22% 8. 8 (0.29 M ) and Hg(0Ac)s (0.37 M ) in AcOH were kept for 23 hr at 75". Only 48 of the allylic esters was recovered with a composition of 21 % 7 and 7 9 z 8.
z
(43) P. D. Sleezer, W. Kitching, S . Winstein, and W. G. Young, unpublished results. (44) E. B. Hershberg, Helc. Chim. Acta, 17,351 (1934). (45) J. M. Van der Zanden and T. R. Rix, Recl. Trac. Chim. PaysBas, 76,75 (1957). (46) D. Pressman and W. G. Young, J . Amer. Chem. Soc., 66, 705 (1944). (47) J. Boeseken and G . Elsen, Recl. Trac. Chim. Pays-Bas, 48, 363 (1929).
Rappoport, Winstein, Young
Allylic Oxidation of Olefins
2328 Table IX.
Vpc Data on the XF-1150Columna Column length, Compound
m
Column T, “C
Injector T, “C
He pressure, psi
Retention time, min
MeCH=CHCHzOAc MeCH(OAc)CH=CHz EtCH=CHCHzOAc EtCH(OAc)CH=CHz MeCH=CHCH(OAc)Me PrCH=CHCH20Ac PrCH( OAc)CH=CHz BuCH=CHCHzOAc BuCH(OAc)CH=CHz n-CjH1lCH=CHCHzOAc n-CgHlICH(OAc)CH=CH2 PhCH=CHCHzOAcb PhCH(OAc)CH=CHzb PhCHzCHzCH=CHCHzOAC
3 3 3 3 3 2
65 65 74 74 74 66 66 80 80 133 133 155 155 154
145 145 160 160 160 150 150 180 180 187 187 190 190 195
10 10 12 12 12 10 10 10 10 16 16 15 15 15
16.9 8.1 18.8 9.8 8.6 21.6 10.0 28.0 13.5 20.5 10.1 20.0 6.0 40.0
2
2 2 3
3 2 2 2
a On 60-80Chromosorb W. 25% column. Other retention times (in minutes); allylbenzene, 1.2;2-acetoxy-l-phenylpropane,6.4; diethyl adipate, 10.0;1,2-diacetoxy-3-phenyIpropane, 60.
Table X. Allylic Acetates from the Oxidation of Olefins by Hg(0Ac)z in Acetic Acid
-
Anal.
Calcd
Allylic acetate
Formula
C
Obsd
H
C
H
Ir (cm-l). in CC14
Me
Nmr (in 6 units) in CCla AcO CHzO CH=CH
CeHioOz 63.13 8.83 63.17 8.82 1722 (s), 1662 (w) 1.68(d) 1.90(s) CeHioOz 63.13 8.83 63.00 9.05 1722 (s), 1631 (m), 1.24(d) 1.95(s) 1420 (m) 1.97(s) C?HilOi 65.59 9.44 65.38 9.50 1722 (s), 1660 (w) 1.01(t) EtCH=CHCHzOAcb C7HizOz 65.59 9.44 65.79 9.39 1722 (s), 1631 (m), 0.97(t)d 1 .97(s) EtCH(OAc)CH=CHz* 1420 (m) PrCH=CHCH20Acb CsH1402 67.57 9.92 67.42 10.03 1722 (s), 1655 (w) 0.91(t)d 1.95(s) CsH140z 67.57 9.92 67.71 9.72 1722 (s), 1630 (w), 0.93(t)d 1 .97(s) PrCH(OAc)CH=CHz 1410 (m) BuCH=CHCHzOAcb CgHieOz 69.19 10.32 69.16 10.28 1722 (s), 1655 (w) 0.91(t)d 1.97(s) CpHieOz 69.19 10.32 69.12 10.32 1722 (s), 1631 (w), 0.91(t)d 1.98(s) BuCH(OAc)CH=CHzb 1418 (m) n-CjH11CH=CHCH20Acc CioHiaOz 70.54 10.66 70.49 10.67 1722 (s), 1675 (m), 0.90(t)d 1.96(s) 1660 (w) n-C5H11CH(OAc)CH=C H Q ) ~ CioHisOz 70.54 10.66 70.68 10.88 1722 (s), 1631 (m), 0.91(t)d 1 ,97(s) 1420 (m) 1.95(s) e CizHiGOz 76.44 7.89 76.41 8.03 1722 (s), 1630 (m), PhCHzCHzCH=CHCHIOAC 1440 (s) MeCH=CHCHIOAc* MeCH( OAc)CH=CHzc
~~
4.32(d) 5.5(m) (m) 4.90-6.00 4.42(d) 5,57(m) 4.90-5.75 (m) 4.43(q) 5.5(m) 4.90-5.80(m) 4.40(4) 5.5(m) 4.97-6.00 (m) 4.40(d) 5.6(m) 4.90-5,90 (m) 4.40(d) 5.64(q)
~~
Only characteristic bands or those differentiating between the primary and secondary esters are given, From the oxidation of the terminal olefin, From the oxidation of the 2-olefin. * A multiplet for the aliphatic protons is observed at 6 1.3-1.6. e CHZprotons are multiplets at 6 2.58; Ph is a singlet at 6 7.15. a
2 (0.06M ) and Hg(OAc)z (0.2M ) in AcOH were kept at 75” for 24 hr. A few crystals of Hgz(OAc)zwere formed. The composition of therecovered ester was 97.2 3 and 2.8% “middle peak.” 3 (0.2M ) and Hg(OAc)z (0.32 M ) in AcOH gave, after 25 hr at 75“,a few needles of HgZ(0Ac)z. The product was 98.2753 and 1.8% “middle peak.” Reaction for 90hr gave Hg, Hgz(OAc)z, “middle peak,” and few additional organic compounds (by vpc) which were not characterized. Oxidation of 4 in AcOH. 4 (5.2g) and Hg(0Ac)t (20.8g) in AcOH (100mi) were refluxed for 50 hr. Hg (9.1g, 7075)was precipitated. The mixture was poured into water, extracted twice with pentane (100 ml), washed (water, aqueous NaHCOa), and dried (NaxS04). The solvent was evaporated and the remainder distilled at 128”( 5 mm) giving 5.35 g (72%) of organic product, 95% of which is 3 (by vpc). Chromatography on silica gel (200 g) gave 4.8g (61%) of 3: nmr (CCl,) 6 1.93(3 H, s, Me), 4.60 (2H, d, J = 5 Hz, CHQ),6.3-6.4(2 H, m, CH=CH), and 7.2( 5 H, broad s, Ph); ir (CCI,) 1770 cm-1. Both ir and nmr are identical with those of an authentic sample. Anal. Calcd for C11HL20z: C, 74.97; H, 6.86. Found: C, 75.05;H, 6.85. A few milligrams of the fraction with a retention time corresponding to 1 ,Z-diacetoxy-3-phenylpropanewere collected. The ir (C=O at 1710 cm-l) was identical with that of an authentic 1,2-diacetoxy-3-phenylpropane.
Journal of the American Chemical Society / 94:7 1 April 5, 1972
2 was collected from the early points of several kinetic runs. It had ir (C=O at 1725 cm-l) and retention time (on two vpc columns) identical with those of the authentic sample: nmr (CClr) 2.00(3H,s,Me),ca.5.2(2H,m,=CHn),ca.6.0(2H,q,CH=CH), 7.27(5 H, s, Ph). Attempts to Prepare the 4-Hg(OAc)z Adduct. On mixing 4 (4.75g) and Hg(OAc)z (13.3 g) in AcOH (20ml) heat was evolved. Stirring continued for 15 min and when all the Hg(OAc)* was dissolved the mixture was poured into ice-water and extracted with methylene chloride (200ml) and the solvent was evaporated. The remaining oil could not be crystallized (benzene-petroleum ether, AcOH, aqueous acetone) or solidify on chromatography (silica gel). After 2 months at room temperature a solid separated, but the analysis ( A n d . Found: C, 19.57; H, 2.04; Hg, 64.35)and the nmr (6 1.60,2.23 (t), and 3.17with relative areas 1 :17.5:7.5) showed that a drastic change in the structure took place. Oxidation of 4 in Aqueous Acetic Acid. The procedure was identical with that in anhydrous acetic acid. Cinnamyl alcohol was identified by its retention time on the XF-1150column (31 min, at 155”,15 psi of He). Reaction of 4 with Acid. 4 (1.41g) was added to H C ~ O I(42 mM) in AcOH (50 ml), and the mixture was kept for 35 hr at 75”. After the usual work-up seven compounds including 4 were formed. The main product (by ir and retention time) is 2-acetoxy-1-phenylpropane. Some 3 was also formed.
2329 Reartion of 3 with Perchloric Acid. To 3 (4.87 g) in AcOH (20 ml), HCIOI (0.52 M ) in AcOH (4 ml) was added. Heat was evolved and the solution turned yellow immediately, then red, and it darkened rapidly. After 1 hr the mixture was poured into water, extracted with methylene chloride (70 ml), washed (aqueous NaHC03), and dried (NanSOa),and the solvent was evaporated. 3 was extracted (pentane) leaving a viscous oil which could not be induced to crystallize (aqueous acetone, methylene chloridepentane) with ir similar to that of 3. Oxidation of the C,Hz, Olefins. A 1 : l mixture of I-olefin and Hg(OAc)? or a 1 : 1 or a 1 :2 mixture of 2-olefin with Hg(0Ac)n in acetic acid was kept at 75" for 7-10 days, or at reflux for several hours. Hg was formed from the 1-olefins and Hgz(0Ac)~from the 2-olefins. The mixture was poured into saturated K2C03 solution, extracted with pentane, and dried (Na2S04),the solvent was evaporated and the esters (which were in a ratio close to the equilibrium value) were separated and analyzed on an XF-1150 column. The best separation conditions are given in Table VIII. The analyses, nmr, and ir of the allylic esters are given in Table IX. In the oxidation of 1-phenyl-3-pentene (8.9 g) by Hg(0Ac)z (18.2 g) in AcOH (35 ml) at 75" for 20 days two nonolefinic compounds were collected, but only the one with the longer retention time was isolated and identified as l-acetoxy-5-phenyl-2-pentene. Olefins from the Oxidation of the Butenes. The reaction mixture from the oxidation of 1-butene (2.2 M ) with Hg(0Ac)~(1.57 M ) in AcOH at 75" for 17 days was poured into cold KzC03 solution, extracted with toluene, and analyzed on a 3-m saturated AgNOaethylene glycol on Firebrick column. At 37", a He pressure of 8 psi, peaks at 2.5 (ll), 8.5 (lo), 9.3 (9), and 46 min (toluene) were observed . Similar analysis from the oxidation mixture of cis-2-butene (0.57 M ) with Hg(0Ac)l; (0.11 M ) for 94 hr at 75" gave a cis-2-butene-
truns-2-butene ratio of ca. 0.33. Traces of 1-butene were also formed, but the peak is mainly covered by the cis-2-butene peak. Kinetic Procedure. (a) By Vpc. Except for the gaseous olefins, stock solutions of the two reactants in acetic acid were prepared. Those of the olefins were stable for months, while those of Hg(OAc), gave some Hgz(OAc)zafter 1 month, and were used within a few days of their preparation. The reagents and the vpc standard were mixed at room temperature and kept at 75". Samples were withdrawn, poured into saturated KzC03 solution, and extracted twice with pentane (50 ml), the extract was washed with saturated K K 0 3 solution (100 ml) and dried (NazS04),the solvent was evaporated at 4.0-60" in cacuo, and the residue was analyzed by V P C . ' ~ The gaseous olefins were absorbed by a suspension of Hg(0Ac)n and their concentrations were determined from the change in weight. (b) By Gravimetry. The reaction was conducted in 25-ml flasks. At predetermined times the contents of the flask were shaken until the mercury formed one droplet. The solution was transferred at the reaction temperature to another 25-ml flask without the Hg droplet. Losses due to transfer were small and were taken into account. The droplet was washed, dried, and weighed. When Hg2(OAc)2was also formed it was separated easily from the droplet, filtered, and dried, and its amount (as Hg) was added to that of the metallic Hg. The kinetics of the solvolysis of 1 was followed by vpc. A sample run is given in Table X. Warning. In preparative vpc of the oxidation mixture some of the organomercury adducts are partially extracted into the ether, and decompose on the vpc column, liberating metallic mercury. (48) The extraction was found to be complete under these conditions. The response of the allylic acetates to the vpc detector was calibrated.
Metal Acetate Promoted Reactions of Allylic Organometallics
T
and
William Kitching,*'" Takashi Sakakiyama,Ib Zvi Rappoport," Paul D. Sleezer,ld S. Winstein," and W. G . YoungIb
Contribution f r o m the Department of Chemistry, University of Queensland, Brisbane, Australia, the Department of Organic Chemistry, Hebrew University, Jerusalem, Israel, and the Department of Chemistry, University of California at Los Angeles, Los Angeles, California 90024. Received July 6, 1971 Abstract: The reactions of the allylic mercurials, trans RCH=CHCHpHgOCOCH3 ( R = CH3 or CBHS),either alone or with added metal acetates, M(OAc),, where M = H g (n = 2), P b (n = 4),T1 (n = 3), and Pd ( n = 2), in acetic acid have been investigated. Product distributions, either extrapolated t o zero time or based on very early observations, have been measured and in the cases of Pb(1V) and Tl(II1) the production of substantial amounts of cis-crotyl acetate is interpreted in terms of SEi' formation of allylic derivatives of these metals, which then demetalate. The dimeric n-crotyl- and n-cinnamylpalladium acetates have also been examined alone, or in the presence of M(OAc), as outlined above, in acetic acid and DMSO-acetic acid (9 :l). Neutral depalladation, L e . , in acetic acid, is suggested t o involve rate-determining formation of a u-allyl species which may then undergo rapidly a number of product-determining depalladations. Reactions with T ~ ( O A Cmay ) ~ involve formation of a r-allyl species (to account for cis product from trans-crotylpalladium complex) as well as direct oxidation of the R complex. This latter path seems quite likely for Pb(OAc)* where the crotyl acetate product is completely trans, although the same stereochemical result would be anticipated for the intervention of a crotyl cation.
T
here are conceptually a n u m b e r of w a y s b y which allylic oxidation of an olefin by M(OAc), (M = Hg(II), Pd(II), TI(III), Pb(1V)) can occur. A particularly attractive pathway involves the formation a n d sub( I ) (a) Address correspondence to this author at the University of Queensland; (b) University of California at Los Angeles; ( c ) Hebrew University; (d) Bristol Laboratories, Syracuse N. Y. 13201 ; (e) Deceased Nov 23, 1969.
s e q u e n t demetallation of an allylic organometallic, a n d this sequence has been suggested for the Hg(OAc)z oxidation of certain olefins in acetic acid.'" In contrast, under some conditions, the most plausible m e c h a n i s m for Pd(OAc)n oxidation of the butenes does not seem to (2) (a) Z. Rappoport, P. D. Sleezer, S. Winstein. and W. G. Young, Tetrahedron Lett., 5119 (1965); (b) W. Kitching, Z. Rappoport. S . Winstein, and W. G. Young,J. Amer. Chem. Soc., 88,2054(1966).
Kitching, et al.
r and n Allylic Organometallics
