Synthesis of Polysubstituted Bicyclo[3.3.1]nonane-3,7-diones from Cyclohexa-2,5-dienones and Dimethyl 1,3-Acetonedicarboxylate

Oxidation of polysubstituted phenols with phenyliodonium diacetate gives cyclohexa-2,5-dienones, which on reaction with dimethyl 1,3-acetonedicarboxylate afford double-Michael-addition derivatives, whose hydrolysis and decarboxylation provides polysubstituted bicyclo[3.3.1]nonane-3,7-diones. For steric and/or electronic reasons, the Michael reaction only works with 3,5-unsubstituted or 3-substituted cyclohexa-2,5-dienones, if the substituent is not an electron-releasing or a good electron-withdrawing group. Hydrolysis and decarboxylation of the double-Michael adducts from 2,4,4- or 2,4,4,6-substituted cyclohexa-2,5-dienones gives only products of partial hydrolysis and decarboxylation, which exist exclusively in the enol form.