Our plan was to attach the exocyclic methylene unit last, so the immediate objective became the ketene acetal 6, which we felt might be reached from 7 or 8 by a proper choice of X (Scheme 1). To restrict double bond formation to C(3a)−C(7a) (see Scheme 1), the route via 8 would probably require that, in the intended synthesis of benesudon, the group X should have a particular stereochemistry (which would depend on the nature of X) relative to both the single hydrogen that would ...
