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 forneceuas respectivas amidas e carbamatos em bons rendimentos. A melhor diastereosseleção facial foiobservada com o uso de (1R,2S,5R)-8-fenilmentol como auxiliar quiral. As amidas e carbamatos2-substituídos foram convertidos nos alcalóides (S)- e (R)-propil pirrolidina e coniina com eficienterecuperação dos auxiliares quiraisThe TiCl4- promoted addition of allyltrimethylsilane to chiral 5- and 6-memberedN-acyliminium ions employing (S)-(+)-mandelic acid, (1R,2S)-trans-2-phenyl-1-cyclohexanol and (1R,2S,5R)-8-phenylmenthol derivatives as chiral auxiliaries occurredwith low to moderate diastereoisomeric ratios (1:1-6:1) to afford 2-substituted amides andcarbamates in good yields. The best diastereoselection was observed with (1R,2S,5R)-8-phenylmenthol as the chiral auxiliary. The 2-substituted amides and carbamates wereconverted to the corresponding alkaloids (S)- and (R)-propyl pyrrolidine and coniine withefficient recovery of the chiral auxiliaries