Diastereoselective synthesis of trans-fused tetrahydropyran derivatives of 5H-dibenzo[a,d]cycloheptene

The epoxides derived from 5H-dibenzo[a,d]cycloheptene and its 2-fluoro derivative were converted into the trans-fused hydropyran-3-one compounds (4aR*,13bS*)-(12-fluoro-)4,4a,9,13b-tetrahydrodibenzo[3,4:6,7]cyclohepta[1,2-b]pyran-3(2H)-one and the corresponding 3-amino derivative via two separate sequences. These involved opening of the epoxide by either a propargyl or allylmagnesium reagent followed by tungsten-mediated cyclisation of the alkynol or OsO4-catalysed transformation into the diol.