The addition of allyltrimethylsilane to cyclic N-acyliminium ions derived from(S)-(+)-mandelic acid and cyclohexyl-based chiral auxiliaries

Journal of the Brazilian Chemical Society

D'Oca, Marcelo G. M.¹  Universidade Estadual de Campinas, Campinas, Brazil¹  Pardini, Vera L.¹  Curi, Denise¹  Comninos, Francisco C. M.¹  Universidade de São Paulo, São Paulo, Brazil¹  Pilli, Ronaldo A.¹ 

关键词: (S)-(+)-Mandelic acid;    cyclohexyl-based chiral auxiliaries;    N-acyliminium ions;    pyrrolidine and piperidine derivatives;   

DOI  :  10.1590/S0103-50532001000400011

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

The introduction of cyclohexyl-based chiral auxiliaries by Corey1 in 1975 and mandelic acid by Trost2 in 1980 stirred the interest for the development of new methodologies for asymmetric carbon-carbon bond formation. Despite that, few asymmetric routes are now available for the regioselective introduction of alkyl groups in the a-nitrogen position of N-acyliminium ions3 employing recoverable chiral auxiliaries4.We were attracted by the possibility of using (S)-(+)-mandelic acid, (1R,2S)-trans-2-phenyl-1-cyclohexanol and (1R,2S,5R)-8-phenylmenthol as chiral auxiliaries during the addition of allyltrimethylsilane to chiral 5- and 6-membered N-acyliminium ions formed in situ from the corresponding 2-methoxy amides and carbamates prepared through anodic oxidation5 (Scheme 1).   Results and DiscussionThe electrochemical oxidation of chiral amides 1a,b and chiral carbamates 2a,b and 3a,b, derived from (S)-(+)-mandelic acid, (1R,2S)-trans-2-phenyl-1-cyclohexanol and (1R,2S,5R)-8-phenylmenthol, respectively, was performed in an undivided cell equipped with a platinum plate anode and a tungsten wire cathode (MeOH, i = 100 mA, J = 25 mA cm-1) to afford the corresponding 2-methoxy mandelic amides 4a,b and 2-methoxy carbamates 5a,b and 6a,b in 62-78% yield, as epimeric mixtures at the a-nitrogen position. The carbon-carbon bond formation step was achieved by treatment of a CH2Cl2 soln. of 4a,b, 5a,b and 6a,b with TiCl4 at -78oC and addition of allyltrimethyl-silane (Scheme 1).Dichloromethane solutions of the epimeric mixtures (4a-b, 5a-b, and 6a-b) were treated with TiCl4 at –78 oC (Scheme 1) to generate the corresponding N-acyliminium ions, followed by the addition of allyltrimehtylsilane. In the

【 授权许可】

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