give the desired doubly anomeric spiroacetal 233 as the major product, along with
four unidentified isomers in a 10:7:3:3 ratio.
2.8 Oxa-Michael Cyclization
The intramolecular addition of a pendant alcohol to a pyrone or chromone has
long been recognized [125] as an effective method for the spirocyclization of
α,β-unsaturated ketone spiroacetals (Scheme 56).
Recently, this approach has been exploited in the synthesis of norhalichondrin B
235 [126] (Scheme 57). Additionally, an oxa-Michael strategy has been used by
Scheme 55 Roush et al.’s synthesis of integramycin model spiroacetal 233 [124]
Scheme 56 Oxa-Michael cyclizations in the synthesis of spiroacetals
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
229
four unidentified isomers in a 10:7:3:3 ratio.
2.8 Oxa-Michael Cyclization
The intramolecular addition of a pendant alcohol to a pyrone or chromone has
long been recognized [125] as an effective method for the spirocyclization of
α,β-unsaturated ketone spiroacetals (Scheme 56).
Recently, this approach has been exploited in the synthesis of norhalichondrin B
235 [126] (Scheme 57). Additionally, an oxa-Michael strategy has been used by
Scheme 55 Roush et al.’s synthesis of integramycin model spiroacetal 233 [124]
Scheme 56 Oxa-Michael cyclizations in the synthesis of spiroacetals
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
229