Steric Control of α- and β-Alkylation of Azulenone Intermediates in a Guanacastepene A Synthesis

The origins of different stercoselectivities observed experimentally in the alkylations of azulenone precursors in the guanacastepene A synthesis have been determined through density functional theory investigations. The optimized transition structures of methylation of two different guanacastepene A precursors show that steric effects, rather than torsional factors that often determine such stereoselectivities, dictate the preferred products observed.