Multifunctionalized alpha,beta-cyclopentenones from C-2 and C-4-ulopyranosyl compounds: a stereospecific rearrangement initiated by base.
Base treatment of O-benzyl protected C-2- or C-4-ulopyranosyl compounds (4 alpha, 4 beta, and 11) by either 10% Et(3)N or 1% K(2)CO(3) in MeOH initiated a beta elimination to afford alpha,beta-unsaturated C-ulopyranosyl compounds (5 alpha, 5 beta, and 12), which further rearranged in a stereocontrolled manner to multifuctionalized alpha,beta-cyclopentenones (6 and 14) in 70-80% yield. Both C-alpha- and C-beta-2-ulosides (5 alpha and 5 beta) produced the same cyclopentenone 6, indicating that a 1,2-enolate is formed prior to the cleavage of the C-5--O bond. Because 6 is racemic, it was probably formed by the intramolecular cycloaldolization of two equally populated enantiomeric intermediates. When treated with 90% Et(3)N in MeOH, 5 alpha yielded almost exclusively 15 (isomer of 6), which was formed by a migration of the double bond in 5 alpha during the previously described rearrangement. Thus either 6 or 15 was the major product, depending on the base used.
Zou
W
W
Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6, Canada. wei.zou@nrc.ca
Wang
Z
Z
Lacroix
E
E
Wu
S H
SH
Jennings
H J
HJ
D003517:Cyclopentanes / Q000737:chemistry*; D005765:Gastrointestinal Agents / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011714:Pyrans / Q000737:chemistry*
D003517:Cyclopentanes; D005765:Gastrointestinal Agents; D011714:Pyrans; C013905:cyclopentenone