α-Diketones as acyl anion equivalents: a non-enzymatic thiamine-promoted route to aldehyde ketone coupling in PEG400 as recyclable medium

By mimicking the peculiar behavior of thiamine diphosphate-dependent acetylacetoin synthase, it has been demonstrated that thiamine hydrochloride 2a and its simple analogue thiazolium salt 2b are able to activate alpha-diketones as acyl anion equivalents in nucleophilic acylations, such as the homo-coupling of alpha-diketones and the hitherto unreported cross-coupling between a-diketones and alpha-ketoesters. These carboligation reactions were optimized under stoichiometric (2a) and catalytic conditions (2b) by using eco-friendly PEG400 as the reaction medium, thus allowing both solvent and thiazolium salt recycling. (C) 2011 Elsevier Ltd. All rights reserved.