α-Diketones as acyl anion equivalents: a non-enzymatic thiamine-promoted route to aldehyde–ketone coupling in PEG400 as recyclable medium
作者:Olga Bortolini、Giancarlo Fantin、Marco Fogagnolo、Pier Paolo Giovannini、Valentina Venturi、Salvatore Pacifico、Alessandro Massi
DOI:10.1016/j.tet.2011.08.056
日期:2011.10
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.
Preparation of Acyloins by Cerium-Catalyzed, Direct Hydroxylation ofβ-Dicarbonyl Compounds with Molecular Oxygen
We report the metal-catalyzed α-hydroxylation of a variety of cyclic and acyclic β-dicarbonylcompounds by molecularoxygen. The decisive advantage of this new method is the use of catalytic amounts of the nontoxic cerium salt CeCl3·7H2O in 2-propanol at ambient temperature. Most of the cyclic substrates 4a−4i give high yields of analytically pure products 5a−5i, and the workup procedure is simple