Intramolecular aldol cyclization of C-4-ulopyranosyl-2′-oxoalkanes controlled by steric effects. Asymmetric synthesis of substituted 8-oxabicyclo[3.2.1]octanones and -octenones and cyclopentenones

Article abstract of DOI:10.1016/j.carres.2004.08.008

Whereas C-2- and 4-ulopyranosyl compounds (C-2- and C-4-ulosides) can be converted to cyclopentenones under base conditions through β-elimination and ring contraction, base-initiated β-elimination of C-glycosyl 2′-aldehydes and 2′-ketones results in the f