Asymmetric Cyclopropanation of Optically Active (1‐Diethoxyphosphoryl)vinyl p ‐Tolyl Sulfoxide with Sulfur Ylides: A Rationale for Diastereoselectivity

The title sulfoxide ( S )‐(+)‐ 1a was found to react with sulfur ylides affording the corresponding cyclopropanes in high yields. With fully deuterated dimethyl(oxo)sulfonium methylide, (CD 3 ) 2 S(O)CD 2 , the cyclopropanation reaction occurred in a highly diastereoselective manner producing the cyclopropane 4a ‐ d 2 as a major diastereomer in which the newly formed quaternary α‐carbon atom is chiral due to isotopic substitution (CH 2 vs. CD 2 ). The diastereomer 4b ‐ d 2 , having the opposite configuration at the α‐carbon atom, was obtained starting form the 2,2‐dideuterio substituted vinyl sulfoxide, ( S )‐(+)‐ 1a ‐ d 2 , and the nondeuterated ylide. The diastereomeric ratio in both reactions was found to be ca. 10:1. The reaction of ( S )‐(+)‐ 1a with diphenylsulfonium isopropylide yielded the cyclopropane (+)‐ 7 as a single diastereomer. X‐ray structural studies of the crystalline 1‐phosphorylvinyl sulfoxide 9 as well as density functional calculations (B3LYP/6‐31G*) on (1‐phosphoryl)vinyl sulfoxides revealed the origin of the experimentally observed diastereoselectivities and allowed us to propose a transition state model for the cyclopropanation reaction of chiral 1‐phosphorylvinyl sulfoxides. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)