Stereoselective Epoxidations and Electrophilic Additions to Partial Ergot Alkaloids and Conformationally-Fixed Styrenes. Experimental and Theoretical Modeling Evidence for the Importance of Torsional Steering as a Stereocontrol Element

Partial ergot alkaloid substrates and related conformationally-fixed styrenes undergo epoxidation, osmium tetraoxide dihydroxylation, and hydrobromination with a level of stereoselectivity which cannot be explained by steric control but is consistent with electrophilic attack to minimize torsional strain. Force-field modeling is consistent with the importance of torsional steering as the dominant stereochemical control element