Tandem Cyclopropanation with CH₂Br₂ under Grignard Conditions

Significance

An efficient cyclopropanation of allylic Mg and Li alcoholates using dibromomethane is described. Reaction rates depend on the substitution pattern of the alcoholates, with α-substituted substrates giving excellent syn selectivity. Furthermore, conjugated aldehydes, ketones and esters have been alkylated using magnesium or lithium reagents yielding intermediate allylic alcoholates which were subsequently cyclopropan­ated using CH₂Br₂.