Base-catalyzed Exchange of Cyclic Diketones under Homoenolization Conditions; Facile Exchange at the Bridgehead and C-7 in 3,3,6,6-Tetramethyl Bicyclo[2.2.1]heptan-2,5-dione

Treatment of 3,3,6,6-tetramethyl bicyclo[2.2.1]heptan-2,5-dione (1) under mild homoenolization conditions (t-BuO − , 175°, 28 h ) results in unusually facile exchange at the bridgehead and C-7. 1,4-Homoenolization to an endo methyl group, converts 1 into 2,2,5-trimethyl bicyclo[3.2.1]octan-3,8-dione(3).