摘要:

988 J.C.S. Perkin INovel Synthesis of @-Substituted P-Diphenylmethylstyrenes from @-Substituted @-Methylstyrenes in the Presence of Palladium(ii) AcetateBy Kimiaki Yamamura, College of General Education, Kobe University, Tsurukabuto, Nada, Kobe, Hyogo 657,Japana-Substituted P-methylstyrenes react with benzene in the presence of palladium(r1) acetate to produce the corre-sponding (€)- and/or (Z)-P-substituted a-diphenylmethylstyrenes in good yields. A mechanism involving a2-substituted 3.3-diphenylpropene intermediate is suggested. The configurations of the products are discussed.PALLADIUM(II) salts have recently attracted much at-tention in relation to their use in organic syntheses.Since Moritani et aZ.1 reported the novel aromaticsubstitution of an olefin in the presence of pal-ladium(I1) salts, numerous reports of similar aromaticH\ / ,c = c\+ Ar-HPd I0AcIzAcOH____cAr \ / /"="\substitution reactions have appeared.For example,similar arylation reactions involving use of arylmercurycompounds,2 triarylphosphines,s and iodobenzenes ,* inthe presence of palladium(I1) salts have been described.Although extensive fundamental studies on these re-actions have been carried out, their application insynthesis has not been extensively investigated. Thispaper reports the preparation of p-substituted P-di-phenylmethylstyrenes from the corresponding p-rnethyl-styrenes by using palladium(11) acetate.We have previously reported the preparation of (E)-and (2) - p-diphen ylmet hyl- P-nitrost yrene from @-methyl-p-nitrostyrene in the presence of palladium(I1) acetate.5This appeared to be the first example of diphenylationof an allylic methyl group brought about by palladium-1 (a) I.Moritani and Y. Fujiwara, Tetrahedron Letters, 1967,1119; (b) M. Watanabe, M. Yamamura, I. Moritani, Y. Fujiwara,and A. Sonoda, Bull. Chem. SOC. Japan, 1974, 47, 1036, andreferences therein.(a) R. F. Heck, J . Amer. Chem. Soc.. 1968, 90, 6618; (b)H. A. Dieck and R. F. Heck, ibid., 1974,@8, 1133, and referencestherein. Letters. 1972, 2829.a K. Kikukawa, T. Yamane, M. Takagi, and T. Matsuda,4 T. Mizoroki, K. Mori, and A. Ozaki, Bull. Chem. SOC. Japan,6 K. Yamamura, S. Watarai, and T. Kinugasa, TetrahedronJ.C.S. CAem. Comm., 1972, 696.1971, 44, 6811975 989(11) acetate.It was then considered of interest to de-termine whether other p-substituted p-methylstyrenesalso reacted with benzene to give the correspondingP-diphenylme t h yls t yrenes.In general method of diphenylation, a mixture ofthe p-methylstyrene derivative and 3 mol. equiv. ofpalladium(11) acetate in acetic acid and large excess ofbenzene was refluxed until precipitation of metallicDiphenylation of p-methylstyrenes in the presence of palladium acetateFound (Calc.) (%)@-Methyl- Yield a -----7 TP.styrene R Products (%) C H N ( C)79.86 5-35 4.4 151(2)-(IIa) 26 3 7 1 79-96 5.35 4-3 10362 (80.0 5.4 4-45)(E)-(W NO, (E) - (114(E) - (If) C,H,4*OMe(p) (E) -(IIf)90.0 6-7543]66 (89.86 5.9)23 89.9 6.7593-65 6-4(93.65 6.35)93.6 6.689.3 6-645 (89.36 6-4)45 89.25 6.652041638610117213311013012011677.7 6.858 4.3 15164 (77.65 6-66 4.3)77.36 5.76 4-25 103(E) - (VW(2) - (VI4 25(i) 1 , r .b (vmaX./cm-l) and (ii) n.m.r.C(6) spectra(i) 1637, 1596, 1447, 1328, 826, 765,695(ii) 8.26 (lH, s, vinyl), 7.32 (SH, s,Ph). 7.23 (lOH, S, Ph), 6-87 (lH, S,-CH’)(i) 160p1525, 1449, 1356, 843, 749,696(ii) 7-28 (lOH, s, Ph), 7.23 (6H, s, Ph),6-13 (lH, d, vinyl, J 1.6 Hz), 6.66(lH, a,-CH<)(i) 1681, 1446, 1415, 1255, 806, 773,692(ii) 10.43br (lH, s, acid), 8.10 (lH,s, vinyl), 7.30 (5H, s, Ph), 7-22(lOH, S, Ph), 6-67 (lH, S, -CH()(i) 1689, 1496, 1446, 1260, 760, 747,692(ii) 9.70br (lH, s, acid), 7.25 (lOH, s,Ph), 7.22 (5H, S.Ph), 6.42 (lH, d,vinyl, J 1.6 Hz), 6-46 (lH, d,(i), 17121446, 1362, 1232, 1095, 736,692(ii) 7.93 (lH, s, vinyl), 7.28 (6H, s,Ph), 7.22 (lOH, S, Ph), 5-63 (lH, S ,-CH’ , 3-57 (3H, s, Me)(i) 1723’1496, 1447, 1368, 747, 698(ii) 7.26 (lOH, s, Ph), 7.22 (SH, S, Ph),6.32 (lH, d, vinyl, J 1.6 Hz), 6.43lH, d,-CH<), 3.46 (3H, s, Me)(i) 1663, 1692, 1487, 1247, 760, 716,688(ii) 7.80-7-20 (21H. m, P h andvinyl), 6-76 (lH, s, -CH<)(i) 1640,1496,1237,966,737,713,696(ii) 7-87-7-03 (20H, m, Ph), 6.69(lH, d, vinyl, J 1.6 Hz), 6.42 (lH,d, -CH<)(i) 1600,1449,1032,770,767,716,699(ii) 7-22 (FiH, s, Ph), 7.10 (lOH, s, Ph),7.03 (6H, s, Ph), 6-86 (lH, s, vinyl),(i) 1599,1494,1076,926,746,735, 696(ii) 7.33-6.80 (20H, m, Ph), 6.20(lH, d, vinyl, J 1.0 Hz), 6.23 (1H.d, -CH<)(i) 1696,1485,1270,1240,1173.1027,690(ii) 7.25-6.62 (19H, m, ArH), 6-86(lH, s, vinyl), 6.72 (lH, s, -CH<),3.67 (3H, s.Me)(i) 1608, 1610, 1292, 1260, 1028, 762,690(ii) 7.26-6-60 (19H, m, ArH), 6-16(lH, d, vinyl, J 1.0 Hz), 6.23 (lH,d,-CH<), 3.68 (3H, s, Me)(i) 1635,1513,1447,908,838,726,696(ii) 8.26 (lH, s, vinyl), 7.23 (BH, s,Ph), 6.87 (IH, s,-CH<)(il 1624. 1460. 1356. 852. 747. 696-CH’)5-82 (lH, S , -CH<)(ii) 7.28 (5H; s, Ph), 6-13 (IH, d,vinyl, J 1.5 Hz), 6-68 (lH, d,-CH<)0 Yields are of isolated and purified products. b KBr disc. c Solvent CDCl,; Me,Si as internal standard. Not isoIated.Estimated D as 2HJ.C.S. Perkin Ipalladium ceased.The results and the physical dataof the products are given in the Table. @-Methyl-styrene itself gave a-methylstilbene, the product ofMe Pd(0AC)Z ICHPh, - PhCH=C, H/c=ck + C6H6 AcOHPh\ /R(la-f 1 (Ea-f)normal phenylation, in 24% yield.6 However, the@-substituted P-methylstyrenes (Ia-f) gave the corre-sponding P-diphenylmethylstyrenes (IIa-f) in 45-66% yields, in one step, along with small amounts ofbiphenyl. The structures of the diphenylation productswere determined from their i.r., u.v., and n.m.r. spectraand elemental analyses. Moreover, the nitro-derivative(E)-(Ia) was identical with a sample prepared inde-pendently by Knoevenagel condensation of benzalde-hyde and 2-nitro-1 ,l-diphenylethane.The reactivity of the P-methylstyrenes was apparentlynot influenced much by the polarity of the a-substituents[cf.compounds (Ie and f)]. Though the use of re-oxidation catalysts such as silver acetate ’ enabled thereaction to proceed catalytically with respect to pallad-ium acetate, it was sometimes difficult to separate theproducts because of the presence of thick slurries ofunchanged palladium acetate. Except in the casesof the ct-methylstilbene derivatives (Ie and f), both(E)- and (2)-isomers of the products were isolated.In the cases of (Ie and f), although only the cis-stilbenederivatives (2)-(IIe) and (2)-(IIf) were isolated thepresence of traces of the (E)-isomers was confirmedby n.m.r. spectroscopy. Compounds (E)-(IIe) and(E)-( IIf) were readily prepared by photoisomerizationof the (,%‘)-isomers.The geometrical configuration ofthe diphenylated products was determined mainly bytheir n.m.r. spectra (Table). For compounds (IIa-d),each of which has a P-substituent exercising a largediamagnetic anisotropy effect, the (E)-isomer, whichhas the vinyl proton and the p-substituent cis to eachother, is expected to show a vinyl proton signal atlower field than the (2)-isomer. Indeed, as previouslyreportedJ6 trans- p-nitrostyrenes, in which the nitro-group and the vinyl proton are cis show the vinylproton signal at 6 8-02-8-36, and cis-P-nitrostyrenesshow the corresponding signal at 6 6.13-766. In thecases of compounds (IIa-d) the vinyl proton chemicalshift differences are large enough (ca. 1.6 p.p.m.) forassignment of configuration.However the correspond-ing differences for compounds (IIe and f) are only 0-6p.p.m., insufficient for definitive assignments. Thisproblem was solved by the observation that the (2)-isomers of (IIa-d) showed long-range coupling betweenthe vinyl proton and the methine proton whereas the(E)-isomers did not; thus the compounds isolated fromthe diphenylation reactions of (Ie) and (If), which didshow such a long-range coupling, were identified as the(2)-isomers. The photoisomerisation products showedK. Yamamura, S. Watarai, and T. Kinugasa, Chem. Letters,1973, 91.no long-range coupling. U.V. data supported theseconfigurational assignments .For the formation of (IIa) from (Ia), we have pre-viously reported the isolation of the intermediate2-nitro-1 l-diphenylpr~pene.~ However the isolationof this compound was not reproducible; instead, when(Ia) was treated with an equimolar amount of palladiumacetate in benzene and acetic acid, a small amount of2-nitro-3,3-diphenylpropene (IVa) was obtained.Thiswas identified from its i.r.J u.v., and n.m.r. spectraand independent preparation. When (IVa) was treatedwith benzene in the presence of palladium acetate inorder to confirm that it was an intermediate, compound(IIa) was produced. However when 2-nitro-1 ,I-di-phenylpropene, prepared independently, was treatedwith benzene in the presence of palladium acetate, noArHgOAc + Pd (OAC)~ __f [ArPdOAcJ+Hg(OAcl,“ 1 H[ArPdOAcJ + ‘c=c’ __t/ \ - A‘ ,c=c\ ’ +[HPdOAc]SCHEME 1/Me C PhPdOAc 1PhCH = C T‘R(Ia-f ) (ma-f 1- C HPPdOAc 3ph MePh’ k Ph’ R(=a-fl (Ya-f 1CPhPdOAc 3 /SCHEME 2evidence for the production of compound (IIa) wasobtained.Heck has suggested a stereospecific reaction mechan-ism involving cis-addition of arylpalladium acetate tothe olefinic double bond and subsequent cis-eliminationof hydridopalladium acetate, for the arylation of anolefin by an arylmercury compound and palladiumacetate * (Scheme 1).Application of this mechanismY. Fujiwara, I. Moritani. M. Matsuda, and S. Teranishi,Tetrahedron Letters, 1968, 3863.R. F. Heck, J . Amer. Chem. Soc., 1969J91,67071975 991to the diphenylation reactions leads to the pathwayshown in Scheme 2. As the first step phenylpalladiumacetate, produced in sit% from benzene and palladiumacetate,8 attacks the p-methylstyrene to give the inter-mediate complex (111) (this could not be isolated).Subsequent cis-elimination of HsPdOAc affords theintermediate (IV).Similar cis-addition of phenyl-palladium acetate to (IV) and subsequent cis-elimin-ation of hydridopalladium acetate affords the product(11). If cis-elimination of HaPdOAc occurs, the pro-duct should be (V). It is considered that (IV) is lessstable thermodynamically than (V) because the formeris the terminal olefin. For cis-elimination of HaPdOAcand HsPdOAc from the intermediate complex (111),the favourable conformations are (A) and (B), and (C)and (D), respectively. It is clear that the formerare more unstable than the latter because of stericinteraction.Consequently, it can be assumed that(IVa-f) are formed preferentially.A mechanism involving direct diphenylation of themethyl group is not thought to be reasonable. If themechanism of Scheme 2 is correct, use of hexadeuterio-benzene instead of benzene as solvent and reactantshould give products of the type (VI) instead of (11).BIn fact, when (Ia) was treated with C,D, in the presenceof palladium acetate under similar conditions, both(E)- and (2)-isomers of (VIa) were obtained instead of(11) (see Table). These products were identified asfollows. The n.m.r. spectrum of (E)-(IIa) showsphenyl group signals a t 6 7.32 (5H) and 7.23 (10H).However (E)-(VIa) shows no peak at 6 7.32 and a singletT. A.Stephenson, S. M. Morehouse, A. R. Powell, J. P.lo H. B. Hass, A. G. Susie, and R. L. Heider, J . Org. Chem.,l1 W. J. Gensler and E. Berman, J. Amer. Chem. Soc., 1968,80,Heffer, and G. Wilkinson, J . Chem. SOC., 1966,3632.1960,15, 8 .4949.&proton peak at 6 7-23.structure of (2)-(VIa) was determined.In a similar manner, theC,D, CH=C'R(34)Thus these diphenylation reactions are not ' direct 'diphenylations of the allylic methyl group but arestepwise reactions.EXPERIMENTAL1.r. spectra were recorded with a Nihonbunko DS-402Gspectrometer, and n.m.r. spectra with a Varian A-60 spectro-meter (CDCl, as solvent and tetramethylsilane as internalstandard).MateriaZs.-Palladium acetate was prepared accordingto the method of Stephenson et aZ.g (3-Methyl-@-nitro-styrene (Ia) ,lo a-methylcinnamic acid (Ib) ,11 and or-methyl-chalcone (Id) l2 were prepared as described in the literature.Methyl a-methylcinnamate (Ic) was prepared by esterifi-cation of (Ib).The or-methylstilbene derivatives (Ie and f)were prepared by a procedure similar to that describedfor the preparation of triphen~lethy1ene.l~General Procedure for the DiPhenyZation of P-Methyl-styrenes.-A mixture of the P-methylstyrene (0.01 mol)and palladium acetate (0.03 mol) in benzene (150 ml) andacetic acid (40 ml) was refluxed with stirring for 20 h.After separation of palladium metal, the mixture waswashed with water and evaporated in V U G ~ O . The residuewas chromatographed over silica gel. Elution withn-hexane gave a small amount of biphenyl; further elutionwith n-hexane-benzene (1 : 1) gave the P-diphenylmethyl-styrene. If some of the starting palladium acetate wasunchanged, reduction to palladium metal by addition ofethanol to the mixture before washing with water facilitatedisolation of the products.Photoisomerization of (2) -(3-DiphenyZmethyZ-(3-phenyZ-styrene [(Z)-(IIe)].-A solution of (2)-(IIe) in benzene wasirradiated with a high-pressure mercury lamp for 4 h,and evaporated in vacuo. Chromatography over silicagel and fractional crystallization from ethanol gave the(E)-isomer, m.p. 110".Under similar conditions (2)-(IIf) gave (E)-(IIf), m.p.120".I thank Professor S. Watarai for discussions, and Miss M.Nishinaka for i.r. measurements and elemental analyses.I also thank Miss M. Sugiura, Kobe Women's College ofPharmacy, for n.m.r. measurements.[4/2049 Received, 4th October, 19741l2 T. Yokoyama and F. Nohara, Bull. Chem. SOC. Jafian, 1966,l3 H. Adkins and W. Zartman, Oyg. Synth., 1943, Coll. Vol. 11,38, 1498.p. 606

ISSN:1472-7781    

DOI:10.1039/P19750000988

出版商:RSC    

年代:1975

数据来源: RSC