Regioselectivity in the intramolecular Heck reaction of a series of cyclic sulfonamides: an experimental and computational study.

Regioselectivity in the intramolecular Heck reaction of a series of N-sulfonyl-2,5-dihydro-3-substituted pyrroles was studied. These substrates are unbiased in terms of the formed ring size of the new heterocycle. Results indicate that high levels of regioselectivity are observed under a range of conditions, and that there is an underlying propensity for carbon-carbon bond formation at the most hindered end of the alkene. For two examples (3-Me and 3-tBu), DFT calculations were performed and indicate that in both cases, the modelled transition state for carbopalladation is energetically lower for the experimentally preferred isomer.