Asymmetric synthesis of cyclopropyl phosphonates using chiral terpenyl sulfonium and selenonium ylides

The asymmetric cyclopropanation of a vinylphosphonate using optically active sulfonium and selenonium ylides derived from (−)-menthol and (+)-limonene was developed. The ylides were generated in situ by the reaction of the corresponding sulfonium or selenonium salt in the presence of potassium carbonate or DBU as a base. The transfer of the CHPh and CHCO2Et groups into the cyclopropane ring showed moderate diastereoselectivity and excellent enantioselectivity (up to 99:1) for the trans- and cis-products. The absolute configuration of phenyl cyclopropyl was assigned based on comparison to their tolyl analogues.

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(1R,2S)-Diethyl 1-[(4-methylphenyl)sulfonyl]-2-phenylcyclopropane]-phosphonateC19H23O2PSEe >98%[α]D22 = −47.2 (c 0.15, acetone)Source of chirality: (R)-(+)-LimoneneAbsolute configuration: (1R,2S)

(1S,2S)-Diethyl-[(4-methylphenyl)sulfonyl]-2-carboethoxycyclopropane]-phosphonateC16H23O7PSEe >98%[α]D21 = −42.8 (c 0.23, acetone)Source of chirality: (R)-(+)-LimoneneAbsolute configuration: (1S,2S)

(1S,2R)-Diethyl-[(4-methylphenyl)sulfonyl]-2-carboethoxycyclopropane]-phosphonateC16H23O7PSEe >98%[α]D21 = −33.7 (c 0.32, acetone)Source of chirality: (R)-(+)-LimoneneAbsolute configuration: (1S,2R)