Abnormal behaviour of allenylsulfones under Lu's reaction conditions: synthesis of enantiopure polyfunctionalised cyclopentenes.

Formal [3+2] cycloadditions of 5-alkoxyfuran-2(5H)-ones 1 and 2 with allenylsulfones 3-5, promoted by different nucleophiles, afford 3-alkoxy-5-arylsulfonyl-3,3 a,6,6 a-tetrahydro-1H-cyclopenta[c]furan-1-ones in good yields with complete control of both regio- and pi-facial selectivity. The incorporation of a sulfinyl group on the furanone ring enhances the reactivity of the furanones and allows the synthesis of optically pure, bicyclic adducts in good yields. Allenylsulfones evolve through a different mechanism to that proposed for allenoates (Lu's reaction) and afford bicyclic adducts in which the sulfonyl group is joined to C-5. This has advantages on the stereochemical control of further reactions leading to enantiomerically pure polyfunctionalised cyclopentenes and cyclopentanes.