Stereoselective Michael additions of phosphorylated allyl carbanions - Synthesis of functionalized cyclopentylphosphonates and phosphane oxides

Dimethyl (2-chloromethyl-2-propenyl)phosphonate (3b) and (tert-butyl)[2-(chloromethyl)-2-propenyl](phenyl)phosphane oxide (3d) were prepared and their reactions with α,β-unsaturated esters 5a-c and ketone 5d, acting as phosphorylated trimethylenemethane equivalents by a [3+2] strategy, were investigated. With the use of LDA in the presence of DMPU, the Michael addition proceeded with high stereoselectivity and regioselectivity to afford methylenecydopentyl-substituted dimethyl phosphonate or (tert-butyl)(phenyl)phosphane oxide derivatives 6a-d and 14(Sp). Compound 3d reacted with 5a-b and 5d to give phosphorous diastereomers 10(Rp) and 11(Sp), 12(Rp) and 13(Sp), and 16(Rp) and 17(Sp), with complete stereoselectivity at the three stereogenic centers of the 5-methylenecydopentanes, all possessing 1,2-trans and 2,3-trans stereochemistry. Formation of open-chain syn adduct 15 and of a 2,3-cis-disubstituted cyclopentane compound 18(Sp) could also be achieved. The stereochemical features of all the products were ascertained by 1D and 2D NMR spectra.