Regiochemistry of S-Alkyl-Substituted Alkynes in Pauson−Khand Reactions. Is a Correlation with X-ray Data and Charge Distribution Calculations of the Co₂(CO)₆-Alkyne Complexes Possible?

Abstract

[reaction: see text] Pauson-Khand reactions (PKR) of RSCtbd1;CR' (6-10) yielded in all cases as the main product the regioisomer with the alkyl-S group disposed alpha to the CO group (16a-22a). Correlation of these results with X-ray data and charge distribution calculations of the corresponding dicobalthexacarbonyl complexes proves that a recently postulated "trans effect" in these complexes is not suitable for predicting the regiochemical outcome of the PKR unambiguously.