isomer. However, transformation to the triol species 13b (doubly anomeric isomer
not shown) allowed selective equilibration to the mono-anomeric spiroacetal 14b
due to favorable chelation of the calcium ion.
Scheme 5 Smith et al.’s synthesis of the CD spiroacetal of spongistatin-1 [26]
Synthesis of 5,6- and 6,6-Spirocyclic Compounds
195