SPIROKETAL EQUILIBRATION - INTERCONVERSION OF 1,6-DIOXASPIRO[4.4]NONANES AND 1,6-DIOXASPIRO[4.5]DECANES - IMPLICATIONS FOR THE SYNTHESIS OFCEPHALOSTATIN
Ju. Jeong et Pl. Fuchs, SPIROKETAL EQUILIBRATION - INTERCONVERSION OF 1,6-DIOXASPIRO[4.4]NONANES AND 1,6-DIOXASPIRO[4.5]DECANES - IMPLICATIONS FOR THE SYNTHESIS OFCEPHALOSTATIN, Tetrahedron letters, 35(30), 1994, pp. 5385-5388
Acid-catalyzed equilibration of spiroketals 55H beta beta and 55H alph
a beta involves a two stage process whereby the 1,6-dioxaspiro[4.4]non
anes can be equilibrated under mild conditions to a pair of 1,6-dioxas
piro[4.5]decanes with preservation of the adjacent C-20 methyl stereoc
enter. Under more forcing conditions, both centers can be equilibrated
in a reaction involving vinyl etheter intermediate 10H.