Stereochemistry of cyclopropyl ketones from the reaction of dimethylsulphoxonium methylide with 3-benzylidenechroman-4-ones

Stereochemical assignments have been made to the cyclopropyl ketones obtained from 3-benzylidenechroman-4-ones by their reaction with dimethylsulphoxonium methylide. The effect of increasing the steric hindrance at the α-position of the double bond on the course of the reaction has been noted and the predominant formation of one isomer is attributed to the steric effect of a ring carbonyl group having an adjacent anionic centre.