The first enantioselective direct aldol addition of N-Boc-oxindoles to polymeric ethyl glyoxylate is presented. The reaction is performed by using as low as 0.1 mol% (DHQ)2PHAL and gives access to a-hydroxycarboxylate derivatives bearing adjacent secondary alcohol and quaternary stereocenters with high levels of diastereo- and enantiocontrol. The use of ethyl glyoxylate in its polymeric form represents an important advantage for synthetic applications and allows us to directly install a C2 unit ready to be converted in useful building blocks. A further one-pot protection/deprotection sequence catalyzed by ZnACHTUNGTRENUNG(ClO4)2·6H2O preserved the a-hydroxycarboxylates from racemization by means of a parasitic alcohol-catalyzed retroaldol reaction.
F. Pesciaioli, P. Righi, A. Mazzanti, C. Gianelli, M. Mancinelli, G. Bartoli, et al. (2011). Cinchona Alkaloid-Catalyzed Enantioselective Direct Aldol Reaction of N-Boc-Oxindoles with Polymeric Ethyl Glyoxylate. ADVANCED SYNTHESIS & CATALYSIS, 353, 2953-2959 [10.1002/adsc.201100499].
Cinchona Alkaloid-Catalyzed Enantioselective Direct Aldol Reaction of N-Boc-Oxindoles with Polymeric Ethyl Glyoxylate
PESCIAIOLI, FABIO;RIGHI, PAOLO;MAZZANTI, ANDREA;MANCINELLI, MICHELE;BARTOLI, GIUSEPPE;BENCIVENNI, GIORGIO
2011
Abstract
The first enantioselective direct aldol addition of N-Boc-oxindoles to polymeric ethyl glyoxylate is presented. The reaction is performed by using as low as 0.1 mol% (DHQ)2PHAL and gives access to a-hydroxycarboxylate derivatives bearing adjacent secondary alcohol and quaternary stereocenters with high levels of diastereo- and enantiocontrol. The use of ethyl glyoxylate in its polymeric form represents an important advantage for synthetic applications and allows us to directly install a C2 unit ready to be converted in useful building blocks. A further one-pot protection/deprotection sequence catalyzed by ZnACHTUNGTRENUNG(ClO4)2·6H2O preserved the a-hydroxycarboxylates from racemization by means of a parasitic alcohol-catalyzed retroaldol reaction.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
