glycoside (62) has been achieved. The synthetic challenge of the B-ring was recognized
and studied initially, resulting in a novel and unique solution to the stereochemical problems
posed involving a [3, 3]-sigmatropic rearrangement of an allylic thionoimidazolide (111).
This chemistry was initially worked out on a model for the ABC-ring system (47) and then
successfully applied to the real system. The success of thissynthesis has enabled the …