Intramolecular 4+3 cycloadditions. Allylic sulfones as precursors to vinylthionium ions

Article abstract of DOI:10.1016/S0040-4039(98)00582-6

Treatment of a THF solution of (E)-3 with n-BuLl followed by quenching with an electrophile generally results in regioselective alkylation alpha to the sulfone with the alkene possessing (E) stereochemistry in the major product. High selectivity for the (E) alkylation product can be achieved in the presence of small amounts of HMPA. When those (E) alkylation products possessing a diene moiety in the side chain are treated with Lewis acids, 4+3 cycloaddition products are formed in good to excellent yields.