Ab initio MO study on [3 + 2] annulation using β-phenylthio-acryloylsilanes with alkyl methyl ketone enolates and its through-space/bond interaction analysis

Ab initio through-space/bond interaction analysis was applied to [3 + 2] annulation based on Brook rearrangement using β-phenylthio-acryloylsilanes with alkyl methyl ketone enolates. An uncertain reaction mechanism, wherein a bulky cyclopentenol with large substituents on the same side of the five-membered ring was obtained as a major product, can be explained by the low activation energy of its reaction pathway. Intramolecular orbital interactions related to the carbanion generated by Brook rearrangement preferentially provide the stabilization of the reaction pathway to the bulky cyclopentenol (major product) compared with that provided to the non-bulky cyclopentenol (minor product). In addition, ab initio molecular orbital calculations suggest the existence of an E/Z conformational inversion after Brook rearrangement. This result accurately explains the loss of the E/Z stereochemical integrity in the starting materials of the experiment.