Carbohydrate Research p. 223 - 231 (2001)
Update date:2022-08-05
Topics:
Zou
Wang
Lacroix
Wu
Jennings
Base treatment of O-benzyl protected C-2- or C-4-ulopyranosyl compounds (4α, 4β, and 11) by either 10% Et3N or 1% K2CO3 in MeOH initiated a β elimination to afford α,β-unsaturated C-ulopyranosyl compounds (5α, 5β, and 12), which further rearranged in a stereocontrolled manner to multifunctionalized α,β-cyclopentenones (6 and 14) in 70-80% yield. Both C-α- and C-β-2-ulosides (5α and 5β) 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% Et3N in MeOH, 5α yielded almost exclusively 15 (isomer of 6), which was formed by a migration of the double bond in 5α during the previously described rearrangement. Thus either 6 or 15 was the major product, depending on the base used.
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