REGIOCHEMICAL CONTROL OF THE RING-OPENING OF 1,2-EPOXIDES BY MEANS OF CHELATING PROCESSES .8. SYNTHESIS AND RING-OPENING REACTIONS OF CIS-OXIDES AND TRANS-OXIDES DERIVED FROM 3-BENZYLOXYCYCLOHEXENE AND 2-BENZYLOXY-5,6-DIHYDRO-2H-PYRAN

The regiochemical outcome of the ring opening of 1,2-epoxides bearing polar remote functionalization through chelation processes assisted by metal ions, was verified in cyclic oxirane systems having the polar functionality in an allylic position to the oxirane ring. The diastereoisomeric cis/trans epoxide pairs 5,6 and 7,8 derived from 3-benzyloxycyclohexene, and 2-benzyloxy-5,6-dihydro-2H-pyran, respectively, were prepared and several of their opening reactions were studied. The regioselectivity observed largely depends on the reaction conditions (standard or metal-assisted) and, interestingly, on the nature of the nucleophile used.