The Prins reaction using ketones: rationalization and application toward the synthesis of the portentol skeleton.

We report a TMSI-promoted Prins cyclization reaction with ketones as carbonyl partners to prepare polysubstituted chiral spirotetrahydropyrans. In the presence of racemic 2-methylcyclohexanone a dynamic kinetic resolution occurred affording one stereoisomer. The observed enantiospecificity has been rationalized by DFT calculation.