Stereoselective Nitrone Additions to Vinyl Phosphine Derivatives: Effect of Phosphorus Substituents on Reaction Diastereoselectivity

Meaningful diastereofacial selectivity in cycloaddition of 2,2-dimethyl-3,4-pyrroline N-oxide (DMPO) to 12 structurally diversified vinylphosphine derivatives 1-12 has been achieved by proper choice of the polar substituent on phosphorus combined with effective steric differentiation of the remaining substituents. The unique sense of induction in all these reactions is consistent with the assumption that vinylphosphorus dipolarophiles prefer an s-cisoid array of C = C - P = X fragments in their reactive conformations. Use of divinylphosphine derivatives in such reactions exemplifies the possibility of synthesizing chiral phosphine oxides and sulfides from prochiral precursors in a highly selective and stereochemically predictable manner. An observation that in P-31 NMR spectra the adducts of type I are uniformly found at lower field than adducts of type II facilitates the stereochemical assignments.