Chemoselective Benzoylations of 1,2-Diols. Reactivity Comparisons of Reagents. Triphenylphosphine-Benzoyl Peroxide and Triphenylphosphine-Diethyl Azodicarboxylate-Benzoic Acid

Article abstract of DOI:10.1021/jo00245a031

The triphenylphosphine-benzoyl peroxide (TPP-BPO) reagent initiates stereospecific benzoylation of secondary carbinol stereocenters with essentially complete inversion of stereochemistry.Monobenzoylations of 1,2-propanediol and styrene glycol with TPP-BPO and triphenylphosphine-diethyl azodicarboxylate-benzoic acid reagents afford a predominance of the more sterically encumbered C-2 benzoate with complete inversion of stereochemistry.Formation of a quintessential 1,3,2λ⁵-dioxaphospholane intermediate, followed by proton-assisted and highly stereoselective ring opening of the phospholanes to isomeric oxyphosphonium ions, allows for Arbusov displacement of triphenylphosphine oxide by benzoate anion.This rationale adequately accounts for both the high chemoselectivity and the stereochemistry of the reactions.