Takai olefination
Abstract
The Takai olefination is a reaction that converts an aldehyde into a vinyl halide, specifically a (E)-vinyl iodide (or bromide), using CHI3 (iodoform) or CHBr3 (bromoform) in the presence of CrCl2. It is one of the most reliable and stereoselective methods for the synthesis of building blocks for cross-coupling chemistry.
Keywords
Aldehyde, Vinyl halide
Category
Aldehyde/Ketone
Mechanism
First, CrCl2 reduces CHI3 through four successive single-electron transfers (SET) steps, generating a nucleophilic organochromium species. This organochromium intermediate then adds to the electrophilic carbonyl carbon of the aldehyde, yielding a transition state in which chromium coordinates to the aldehyde oxygen. The resulting intermediate subsequently undergoes anti elimination with loss of CrCl2 and a chromium oxide species, directly yielding the (E)-vinyl iodide. The (E)-selectivity arises from the anti elimination geometry, which places the R group and the iodine atom on opposite sides of the newly formed double bond.
