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

Abstract

A adição de aliltrimetilsilano, promovida por TiCl4, a íons N-aciliminios cíclicos de 5- e 6- membros derivados do ácido (S)-(+)-mandélico, (1R,2S)-trans-2-fenil-1-cicloexanol e (1R,2S,5R)- 8-fenilmentol ocorreu com baixas a moderadas razões diastereoisoméricas (1:1-6:1) e forneceu as respectivas amidas e carbamatos em bons rendimentos. A melhor diastereosseleção facial foi observada com o uso de (1R,2S,5R)-8-fenilmentol como auxiliar quiral. As amidas e carbamatos 2-substituídos foram convertidos nos alcalóides (S)- e (R)-propil pirrolidina e coniina com eficiente recuperação dos auxiliares quirais.The TiCl4 - promoted addition of allyltrimethylsilane to chiral 5- and 6-membered N-acyliminium ions employing (S)-(+)-mandelic acid, (1R,2S)-trans-2-phenyl-1- cyclohexanol and (1R,2S,5R)-8-phenylmenthol derivatives as chiral auxiliaries occurred with low to moderate diastereoisomeric ratios (1:1-6:1) to afford 2-substituted amides and carbamates in good yields. The best diastereoselection was observed with (1R,2S,5R)-8- phenylmenthol as the chiral auxiliary. The 2-substituted amides and carbamates were converted to the corresponding alkaloids (S)- and (R)-propyl pyrrolidine and coniine with efficient recovery of the chiral auxiliaries.