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)