Synthesis, reactions, and properties of 2,8-didehydronoradamantane derivatives

2,8-Didehydronoradamantan-9-one (2) was readily prepared by oxa-di-pi-metha ne photorearrangement of brend-4-en-2-one ill. Other new 9-substituted 2,8- didehydronoradamantanes have also been prepared from 2, [i.e. 2,8-didehydro noradamantan-9-ol (3) and tosylhydrazone 4] and the ring-opening reactions have been studied. In acidic media, 2,8-didehydronoradamantan-9-ol (3) rear ranges to the corresponding 2-substituted brend-4-ene derivatives. Exclusiv e formation of exe-2-substituted brend-4-enes supports the formation of a b ridged bicyclobutonium ion. However, treatment of ketone 2 with PCl5 procee ds through a concerted mechanism by cleavage of the C-1-C-2 bond in 2 to gi ve exo-2,5-dichlorotricyclo[4.2.1.0(3,8)]non- (6). The tricyclo[4.2.1.0(3,8 )]nonane skeleton was also obtained by photochemically induced electron tra nsfer reduction of 2 and reduction of 2 with Li/NH3, as well as by reductio n of tosylhydrazone 4 with both NaBH3CN and BH3 X THF. On the other hand, W olff-Kishner reduction of 2 gave the nonrearranged product, 2,8-didehydrono radamantane (10).