Cinchona Alkaloid-Catalyzed Enantioselective Direct Aldol Reaction of N-Boc-Oxindoles with Polymeric Ethyl Glyoxylate

✍ Scribed by Fabio Pesciaioli; Paolo Righi; Andrea Mazzanti; Chiara Gianelli; Michele Mancinelli; Giuseppe Bartoli; Giorgio Bencivenni

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 229 KB
• Volume: 353
• Category: Article
• ISSN: 1615-4150
• DOI: 10.1002/adsc.201100499

✦ Synopsis

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 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 C 2 unit ready to be converted in useful building blocks. A further one-pot protection/deprotection sequence catalyzed by ZnA C H T U N G T R E N N U N G (ClO 4 ) 2 •6 H 2 O preserved the a-hydroxycarboxylates from racemization by means of a parasitic alcohol-catalyzed retroaldol reaction.