The solvolytic behaviour of exo- and endo-1,5-dimethyl-9-oxobicyclo-[3,3,1 ]nonan-2-yl toluene-p-sulphonates

Abstract

The buffered acetolysis of the exo-title compound gives mainly 1,5-dimethylbicyclo[3,3,1]non-2-en-9-one (9)(75%) and the corresponding exo- and endo-2-acetates (6 and 7; R = Ac)(13%) in the ratio of 1:12, whereas similar treatment of the endo-title compound gives 2,6-dimethylbicyclo[4,2,1]non-2-en-9-one (11)(51%), the corresponding tertiary acetates (12 and 13; R = Ac)(16%) accompanied by the enone (9)(8%), and the acetates (6 and 7; R = Ac)(25%) in a ratio of >24:1. These results are best explained in terms of ion-pair mechanisms. The fact that unbuffered acetolysis of both acetates (6 and 7; R = Ts) gives 1,4-dimethylindane (8) and 2-acetyl-5-methylbicyclo[3,3,0]oct-1-ene (10) in the same ratio (4:5) but in different yields (9 and 46%) suggests that (8) and (10) are both acid-catalysed rearrangement products of (11 ).