STEREOSELECTIVE SYNTHESIS OF A BICYCLIC KETOOXETANE VIA A THIONIUM ION-MEDIATED CYCLIZATION REACTION

The synthesis of a bicyclic ketooxetane using as the key step the ethy laluminium dichloride-mediated cyclisation of a Z-silyl enol ether ont o a thionium ion 'trigger' attached to a five-membered carbocyclic tem plate is described. Attempted cyclisation of the analogous substrate p ossessing a six-membered ring did not afford the oxetane, but instead the product of 1,2-hydride shift, The mechanism of this unexpected tra nsformation was conclusively established by analysis of the products o f attempted cyclisation of a deuterium-labelled substrate.