Protection of the hydroxy group of the medium-ring hydroxy ketone, 5-hydroxycyclooctanone (1HK), can be achieved with an alcohol and hydrochloric acid, although the substrate predominately exists as the transannular hemiacetal 1HA. The reaction is explained by a mechanism, which includes a 1,5-hydride shift as an essential step.
medium rings - transannular acetals - protection - transannular reaction - hydride shift