A comparative study on the 1,3-dipolar cycloadditions of diazomethane and bis(diisopropylamino)phosphinodiazomethane to chiral electron-deficient olefins: Reactivity and diastereoselectivity

Abstract

The 1,3-dipolar cycloadditions of bis(diisopropylamino)phosphinodiazomethane, 10, to chiral electron-deficient olefins have been investigated for the first time. The results have been compared with those corresponding to the reactions of diazomethane and the same or similar substrates. The experimental observations have been rationalized by DFT theoretical calculations. Diazomethane has been shown to be more reactive than 10 in all cases. The dipolarophiles include compounds synthesized from D-glyceraldehyde acetonide and (-)-verbenone. The latter compounds, bearing a gem-dimethylcyclobutane moiety, are less reactive than those derived from D-glyceraldehyde bearing a dioxolane ring. The influence of the Z/E geometry of the double bond on the reactivity and the π-facial diastereoselectivity has been investigated. Thus, in the reactions of diazomethane, the diastereoselectivity is not dependent on the Z/E stereochemistry but the reactivity is lower for (E)-cyclobutyl derivatives than for their Z isomers. In the reactions between 10 and the glyceraldehyde derivatives, the E isomers are less reactive than the Z ones and afford adducts with poor facial diastereoselectivity due to unfavorable interactions between the reactants in the corresponding transition states.