Aprotic Conjugate Addition of Allyllithium Reagents Bearing Polar Groups to Cyclic Enones. 1. 3-Alkylallyl Systems

The conjugate addition of lithiated (E)- and (Z)-oct-2-enyl sulfoxides and phosphine oxides, but-2-enyl sulfoxides, phosphine oxides and phosphonates, and 3, 3-dimethylallyl and allyl sulfoxides to cyclic enones has been examined. The E and Z carbanions react in highly diastereoselective fashion with five-membered cyclic enones to deliver respectively syn and anti vinylic sulfoxides, phosphine oxides, and phosphonates. Hexamethylphosphoric triamide has no regiochemical influence on these reactions. The regiochemical and stereochemical outcomes of these reactions are rationalized in terms of planar lithiated reagents in which Li⁺ is bound to oxygen attached to sulfur or phosphorus of the polar group and a 10-membered “trans-decalyl“. “trans-fused chair-chair”-like transition-state model in which the lithiated reagent adopts an endo orientation over one face of the enone such that for the E reagent, the 3-alkyl group is pseudoequatorial, and for the Z, pseudoaxial.