REGIOCHEMICAL CONTROL OF THE RING-OPENING OF 1,2-EPOXIDES BY MEANS OFCHELATING 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 f unctionality in an allylic position to the oxirane ring. The diastereo isomeric cis/trans epoxide pairs 5,6 and 7,8 derived from 3-benzyloxyc yclohexene, and 2-benzyloxy-5,6-dihydro-2H-pyran, respectively, were p repared and several of their opening reactions were studied. The regio selectivity observed largely depends on the reaction conditions (stand ard or metal-assisted) and, interestingly, on the nature of the nucleo phile used.