Carbonylation of organomagnesium compounds: catalysis by hexamethylphosphoric triamide

Abstract

Carbonylation of Grignard derivatives (RMgX), very slow in ether, is markedly accelerated when adding (or using neat) hexamethylphosphoric triamide (HMPT). Typically, uptake of CO is completed within a few minutes at room temperature and at ca. 30 atm. Product composition is dependent on R, solvent composition (RMgX : HMPT ratio), and on the presence of electrophiles such as ‘extra’ alkyl halide. Synthetically attractive methods for preparing several types of (hydroxy)ketone derivatives [(1), (4), and (5)] from primary alkyl halides are outlined. Other types of R(Mg)X mostly lead to acyloins RCH(OH)C(O)R. Evidence for the formation of RCOMgX, or equivalent(s), as ‘first’ intermediates is presented. The overall mechanism is discussed. Products, and effects of HMPT on rate and product composition, can satisfactorily be explained via nucleophilic addition and substitution steps, deprotonation, and reduction reactions, leading to Mg salts of enols as ‘final’ intermediates.