REGIOCHEMICAL CONTROL OF THE RING-OPENING OF 1,2-EPOXIDES BY MEANS OFCHELATING PROCESSES .7. SYNTHESIS AND RING-OPENING REACTIONS OF CIS-OXIDE AND TRANS-OXIDE DERIVED FROM 2-(BENZYLOXY)-3,6-DIHYDRO-2H-PYRAN

The regiochemical outcome of the ring opening of 1,2-epoxides bearing polar remote functionalities through chelation processes assisted by m etal ions was verified in a conformationally semirigid cyclic oxirane system in which the polar functionality is both directly inserted into the cyclic system and present on the cyclic system itself. Diastereoi someric cis 4 and trans epoxide 5, derived from 2-(benzyloxy)-3,6-dihy dro-2H-pyran, were prepared and some of their opening reactions (azido lysis, aminolysis, Cl- addition, and LiAlH4 reduction) were studied. T he regioselectivity observed is largely dependent for both 4 and 5 on the opening (standard or metal-assisted) reaction conditions, and a re gioalternating process is almost obtained.