Regioselective Single and Double Conjugate Additions to Substituted Cyclohexa-2,5-dienone Monoacetals

A series of quinone monoacetals bearing electron-withdrawing groups was treated with diethyl malonate and other bifunctional nucleophiles
in the presence of KO-t-Bu in THF. Reactions of ethyl 3-nitropropionate or diethyl malonate resulted in single conjugate addition adducts.
When ethyl acetoacetate was used as a nucleophile, bridged bicyclic products were obtained in good yields. The regiochemistry of conjugate
addition was dependent on the quinone monoacetal substitution.