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Cinchona Alkaloid‐Catalyzed Enantioselective Direct Aldol Reaction of N ‐Boc‐Oxindoles with Polymeric Ethyl Glyoxylate
Author(s) -
Pesciaioli Fabio,
Righi Paolo,
Mazzanti Andrea,
Gianelli Chiara,
Mancinelli Michele,
Bartoli Giuseppe,
Bencivenni Giorgio
Publication year - 2011
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201100499
Subject(s) - chemistry , stereocenter , enantioselective synthesis , glyoxylate cycle , aldol reaction , racemization , organic chemistry , cinchona , alcohol , catalysis , cinchona alkaloids , combinatorial chemistry , organocatalysis , enzyme
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) 2 PHAL and gives access to α‐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 C 2 unit ready to be converted in useful building blocks. A further one‐pot protection/deprotection sequence catalyzed by Zn(ClO 4 ) 2 ⋅6 H 2 O preserved the α‐hydroxycarboxylates from racemization by means of a parasitic alcohol‐catalyzed retroaldol reaction.