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Organocatalysis for the Acid‐Free O ‐Arylidenation of Carbohydrates
Author(s) -
Geng Yiqun,
Faidallah Hassan M.,
Albar Hassan A.,
Mhkalid Ibrahim A.,
Schmidt Richard R.
Publication year - 2013
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201301116
Subject(s) - chemistry , squaramide , thiourea , orthoester , acetal , reagent , benzaldehyde , organic chemistry , organocatalysis , catalysis , enantioselective synthesis
Methyl glycopyranosides of glucose, galactose, and mannose, their 2,3‐di‐ O ‐benzyl‐protected derivatives, as well as the unprotected sugars react with p ‐methoxybenzaldehyde dimethyl acetal ( 3 ) and with benzaldehyde dimethyl acetal ( 7 ) as reagents in the presence of thiourea 1 or squaramide 2 as the organocatalyst to afford regioselectively 4,6‐ O ‐arylidenated derivatives 5 and 8 . With an excess amount of 3 or 7 , diarylidenated derivatives are also obtained. In situ formation of acetals of type 3 and 7 from corresponding aldehydes 10 and 13 in the presence of an orthoester and organocatalyst 1 or 2 can be used to generate 5 and 8 directly from the aldehydes. Some substrates also lead to mixed orthoesters with this procedure. The reaction courses are discussed.