Chiral ligands derived from abrine. Part 5: Substituent effects on asymmetric induction in enantioselective addition of diethylzinc to benzaldehyde catalyzed by chiral oxazolidines possessing an indole moiety
摘要:
A number of the indole-containing chiral oxazolidines possessing the gem-di-p-tolyl and gem-di-o-tolyl groups at C-5 were synthesized from abrine and the effects of the C-5 and C-2 substituents on the asymmetric induction in catalytic enantioselective addition of diethylzinc to benzaldehyde were examined. A working model is proposed to rationalize the asymmetric catalysis by these chiral oxazolidines. (C) 1998 Elsevier Science Ltd. All rights reserved.
Chiral ligands derived from Abrine. 1. Synthesis of sec- and tert-β-amino alcohols and catalysis for enantioselective addition of diethylzinc toward aromatic aldehydes
Chiral ligands derived from abrine. Part 6: Importance of a bulky N-alkyl group in indole-containing chiral β-tertiary amino alcohols for controlling enantioselectivity in addition of diethylzinc toward aldehydes
作者:Wei-Min Dai、Hua-Jie Zhu、Xiao-Jiang Hao
DOI:10.1016/s0957-4166(00)00189-0
日期:2000.6
A number of chiral beta-amino alcohols possessing a 3-indolylmethyl group have been synthesized from the alkaloid (S)-abrine and elucidated for potency in the catalytic enantioselective ethylation of PhCHO with Et2Zn. In general, the secondary amines 15a-d bearing a dialkylhydroxymethyl group induced (R)-1-phenyl-1-propanol, whereas 15e-g and 18 bearing a diarylhydroxymethyl group favored the (S)-enantiomer. In contrast, the beta-tertiary amino alcohols 20b d and 21 produced (R)-1-phenyl-1-propanol. regardless of the substituents at the carbon bearing the hydroxy group. Enantiomeric excess of 87.5% was obtained for (R)-1-phenyl-1-propanol using ligand 21 as the promoter. Eleven substituted benzaldehydes and naphth-aldehydes were examined for enantioselective ethylation by using 21 and the chiral alcohols were obtained in 93-97% ee, except for o-BrC6H4CHO and p-Me2NC6H4CHO. Excellent enantioselectivity was also observed in the ethylation of cyclohexanecarboxaldehyde (94.8% ee) and 2-thiophenecarboxaldehyde (94.9% ee) by using catalytic 21. The anti 5/4/4-fused tricyclic TS I was proposed to rationalize the asymmetric induction. The diethylhydroxymethyl and N-2-t-butylethyl groups are believed to enforce the preference for the anti-TS(R) I and it results in high enantioselectivity. (C) 2000 Elsevier Science Ltd. All rights reserved.
Chiral ligands derived from Abrine. 1. Synthesis of sec- and tert-β-amino alcohols and catalysis for enantioselective addition of diethylzinc toward aromatic aldehydes
作者:Wei-Min Dai、Hua Jie Zhu、Xiao-Jiang Hao
DOI:10.1016/0957-4166(95)00236-i
日期:1995.8
Chiral ligands derived from abrine. Part 5: Substituent effects on asymmetric induction in enantioselective addition of diethylzinc to benzaldehyde catalyzed by chiral oxazolidines possessing an indole moiety
A number of the indole-containing chiral oxazolidines possessing the gem-di-p-tolyl and gem-di-o-tolyl groups at C-5 were synthesized from abrine and the effects of the C-5 and C-2 substituents on the asymmetric induction in catalytic enantioselective addition of diethylzinc to benzaldehyde were examined. A working model is proposed to rationalize the asymmetric catalysis by these chiral oxazolidines. (C) 1998 Elsevier Science Ltd. All rights reserved.