Transformation of cis-Epoxy Compound to cis-2,3-Disubstituted Oxane and Investigation on Propagation Step in the Ring-Expansion Reactions of cis,trans-Diepoxy Systems

Conversion of cis-epoxy compounds by successive ring-expansion reaction into trans-fused cyclic ethers was examined from both the initiation step and the propagation step. The ring-expansion reaction of cis-4,5-epoxy compounds containing a leaving group on C-1 was attempted as a unit process for the successive reaction. When a chloromesyl group was used as a leaving group, the ring expansion proceeded to give an oxane derivative (endo-type product) preferentially. On the other hand, investigation of the propagation step was carried out with respect to epoxy oxane derivatives. It was clarified that the ring-expansion reaction of cis-2,3-disubstituted oxane derivatives provided spiro acetals as products, not the desired trans-fused cyclic ethers, owing to the reaction pathway triggered by 1,2-hydride rearrangement.