Regio- and Stereoselective Double Addition of Anionic C-Nucleophiles to Cobalt-Stabilized Acetylenedicarbaldehyde

Though intrinsically unstable, Gorgues’ acetylenedicarbaldehyde is an appealing, highly functional C4 synthon, which can be stabilized by η2 complexation to a Co2(CO)6 unit. In contrast to the homologous dibenzoylacetylene complex, it can be used as a normal, doubly electrophilic, non-conjugated γ-dicarbonyl substrate toward alkyl-, aryl-, and alkynyllithium compounds or magnesium bromides; these anionic C-nucleophiles do not predominantly attack at the metal-carbonyl center. The 1,4-dialkyl- and 1,4-diphenylbut-2-yne-1,4-diol products are obtained with significant meso/dl diastereoselectivity (4−66% de), which can be explained by a simple model based on X-ray diffraction data and MM calculations. The alkyl- and arylmagnesium bromide reactants are more selective than their lithium counterparts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)