THE TRANSANNULAR REARRANGEMENT OF 5-CYCLODECYNONE

The acid-catalyzed rearrangement of 5-cyclodecynone (1) to bicyclo[4.4.0]-1(6)-decen-2-one (5) has been investigated via C-13 and deuterium labeling experiments, which showed that the transannular rearrangement proceeds by a mechanism not involving an enol of 5-cyclodecynone. Subjecting 5-cyclodecynone to NBS in ethyl ether resulted in the formation of a dibromooxetane 21 which arose from a bromo allylic alcohol 20 formed from 5-cyclodecynone and HBr. The chloro allylic alcohol 28 was formed from HCl and was subsequently converted to enone 5. Pathways were investigated using AM1 calculations. As a result, a modified mechanism consistent with all the experimental data is proposed for the acid-catalyzed rearrangement of 1 to 5.