Solvolysis of exo- and endo-Tricyclo[3,3,0,0^2,8]oct-4-yl p-Toluenesulphonates

Abstract

The structure of endo-tricyclo[3,3,0,0^2,8]octan-4-ol (3; X = OH) has been confirmed by hydrogenolysis which affords the known alcohols endo- (equatorial)-bicyclo[3,2,1]octan-2-(11) and cis-bicyclo[3,3,0]octan- anti-2-ol (12). Hydrolysis of derived p-toluenesulphonate (3; X = OTs) in 70% aqueous acetone at 21.6° proceeds with a first-order rate constant of 6.67±0.21x10^-4s^-1, and under buffered conditions yields endo- tricyclo[3,3,0,0^2,8]octan-4-ol (3; X = OH) as the only observable product. The results suggest that ionization of (3; X = OTs) proceeds with participation of the C 1 to C2 bonding electrons to give the intermediate trishomocyclopropenyl cation (4) which suffers stereospecific solvent capture to yield (3; X = OH). The results obtained with the monodeuterated isotopomer (17; X = OTs) are consistent with this mechanism. Hydrolysis of exo- tricyclo[3,3,0,0^2,8]oct-4-yl p-toluenesulphonate (5; X = OTs) is a little slower than its epimer(3; X = OTs), and proceeds with a first-order rate constant of (1.9±0.04)x 10^-4s^-1 at 49.9° in 70% aqueous acetone. The mechanism in this instance appears to involve anchimerically assisted ionization and subsequent formation of the intermediate tricyclo[3,2,1,0^2,7]oct-6-yl cation (24)which yields a characteristic mixture of products consisting of endo-tricyclo[3,2,1,0^2,7]octan-6-ol(20; X = OH) (mainly), its epimer (21; X = OH), exo-bicyclo[3,2,1]oct-6-en- 2-ol (18; X =OH)and exo-bicyclo[2,2,2]oct-5-en-2-ol (19; X = OH).    A reinvestigation of the buffered acetolysis of exo- tricyclo[3,2,1,0^2,7]oct-6-yl p-nitrobenzoate(21; X = OPnb) has shown that, contrary to previous conclusions, there is no leakage from the L series to the G series in this system.