13C magnetic resonance studies 133. An examination of the effect of conformation on β-enolization in some bicyclo[3.2.1]octan-2-ones

Abstract

To assess the influence of the conformation of the cyclohexanone moiety in bicyclo[3.2.1]octan-2-ones on the reactivity for β-enolate rearrangement, the behavior of three derivatives under typical homoenolization conditions has been examined for comparison with 3,3-dimethylbicyclo[3.2.1]octan-2-one (1), which was known to be smoothly converted to the [3.3.0] isomer 2. For this purpose, endo-3-tert-butyl-exo-3-methylbicyclo[3.2.1]octan-2-one (8), endo-9-tert-butyl-exo-9-methyl-exo-tricyclo[5.3.1.02,6]undecan-8-one (9), and 9,9-dimethyl-endo-tricyclo[5.3.1.02,6]undecan-8-one (10) were prepared and treated with [Formula: see text] for prolonged periods. Each is much less reactive than 1. The relative orientations of the carbonyl groups with respect to the sites for β-enolization were determined by molecular mechanics (MM2) calculations. 1H/2H exchange in 9 and 10 was also examined under strongly basic conditions at 185 °C.