Evidence for concerted processes in the course of the homoallenylic transposition

The hydrolysis of β-allenic tosylates produces mainly 2-methylenecyclobutanols resulting from a homoallenylic participation along with isomeric 2-methylenecyclobutanol minor products coming from a 1234–1243 rearrangement. Structures of various cyclopropylvinyl carbocations involved in the course of the hydrolysis have been determined by computational studies. For acyclic tosylates, the hydrolysis of one β-deuterated allenic tosylate confirmed the nucleophilic attack on the corresponding nonclassical carbonium ion before its evolution to a more stable cyclopropylvinyl carbocation. In the case of one cyclic β-allenic tosylate, the structure of the products has been checked by the use of deuterated isotopomer.