Stereoselectivity of Michael Addition of P(X)–H-Type Nucleophiles to Cyclohexen-1-ylphosphine Oxide: The Case of Base-Selective Transformation

Michael addition of phosphorus nucleophiles to the unsymmetrically substituted tert-butyl(1,4-cyclohexadien-3-yl)phosphine oxide and its derivatives has been described. The addition proceeds with the formation of the mixture of two isomeric products with good yield and diastereoselectivity. The reaction of tert-butyl(cyclohexen-1-yl)methylphosphine oxide with phosphorus nucleophiles is base sensitive and might afford two epimers which differ at one chirality center. The absolute configuration of the products has been assigned on the basis of conformational and 1H NMR analysis, and the mechanism of the reaction has been discussed. The Michael addition of phosphorus nucleophiles is postulated to proceed with or without consecutive epimerization of two α-carbanions.