Synthesis of β-dicarbonyl compounds using 1-acylbenzotriazoles as regioselective C-acylating reagents

Enolate acylations often form mixtures of O- and C-acylation products.(1) The nature of the electrophile, metal counterion, solvent, the reaction temperature, reagent stoichiometry, or structure of the substrate itself have all been shown to influence significantly the regioselectivity of such acylations.(2) Carbon acylations have been widely studied and reviewed.(2,3) The regioselective synthesis of 1,3-diketones and 1,3-ketoesters by the C-acylation of simple ketone enolates has been investigated using a plethora of acylating reagents, including formates and oxalates,(3) anhydrides,(4a) acid chlorides,(4b) dialkyl carbonates,(4c,d) methyl methoxymagnesium carbonate,(4b) N-acylimidazoles,(4f) and more recently, acyl cyanides.(4g,h) Indirect methods for carbon acylation utilized for the efficient preparation of beta-dicarbonyl compounds include (i) migration of the acyl group from the enol ester,(5a) (ii) umpolung-type carbonyl anion synthons,(5b) (iii) acylation of silyl enol ethers,(5c) and (iv) oxidation of beta-hydroxycarbonyl derivatives, obtained by aldol condensations of carbonyl compounds with aldehydes.(5d).