Enantioselective aldol reaction with a bromofluoroketene silyl acetal catalyzed by a chiral Lewis acid
摘要:
Bromofluoroketene silyl acetal 1 was prepared in pure form. Aldol reactions of 1 with achiral aldehydes catalyzed by chiral Lewis acid 2 proceeded with high enantioselectivity to give optically active syn- and anti-alpha-bromo-alpha-fluoro-beta-hydroxy esters 3a-h, respectively (up to 99% ee). (C) 1997 Elsevier Science Ltd.
Enantioselective aldol reaction with a bromofluoroketene silyl acetal catalyzed by a chiral Lewis acid
摘要:
Bromofluoroketene silyl acetal 1 was prepared in pure form. Aldol reactions of 1 with achiral aldehydes catalyzed by chiral Lewis acid 2 proceeded with high enantioselectivity to give optically active syn- and anti-alpha-bromo-alpha-fluoro-beta-hydroxy esters 3a-h, respectively (up to 99% ee). (C) 1997 Elsevier Science Ltd.
Reaction of aldehydes with bromofluoroketene silyl acetal 1 in the presence of 20 mol% chiral Lewis acid 2 proceeds with enantio- and diastereoselectivities at -20 °C to afford optically active anti-α-bromo-α-fluoro-β-hydroxy esters 3a-f (up to 89:11 anti:syn, up to 93% ee).
The aldol reaction of aldehydes with bromofluoroketene ethyl trimethylsilyl acetal in the presence of a catalytic amount of a chiral Lewis acid at -78 degrees C provides a mixture of the corresponding syn- and anli-alpha-bromo-alpha-fluoro-beta-hydroxy esters with high enantioselectivities (up to 99% ee). Reaction temperature has a great influence on the stereoselectivity. The aldol reaction at -20 degrees C proceeds with high enantio- and diasteteoselectivities to preferentially afford the anti-aldols having opposite signs of optical rotation to those at -78 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.
Enantioselective aldol reaction with a bromofluoroketene silyl acetal catalyzed by a chiral Lewis acid
Bromofluoroketene silyl acetal 1 was prepared in pure form. Aldol reactions of 1 with achiral aldehydes catalyzed by chiral Lewis acid 2 proceeded with high enantioselectivity to give optically active syn- and anti-alpha-bromo-alpha-fluoro-beta-hydroxy esters 3a-h, respectively (up to 99% ee). (C) 1997 Elsevier Science Ltd.