Synthesis of Bicyclic Unsaturated Tetrahydrofurans

The ready deprotonation of the vinyl aminosulfoxonium salts 46 with a strong base at the a-position prompted a study of their reactions with weaker bases. It was speculated that in this case a vinyl-allyl isomerization of 46 might occur, followed by an intramolecular substitution of the allyl aminosulfoxonium salt 

Tetrahydrofurans 53 should be of synthetic interest because of the many natural products containing a bicyclic tetrahydrofuranoid skeleton or structural element [30]. The double bond would allow further synthetic transformations. While the chances of a regioselective isomerization of 46 to the allyl aminosulfoxonium salts 52 seemed to be good, the prospects of a cyclization of the latter with formation of 53 were considered to be less promising because of the poor nucleophilicity of the silyloxy group. 

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