Acyl radical cyclizations in synthesis. Part 3. Synthesis of (±)-trans-3,5-bis-(t-butyldimethylsiloxy)-2-methylenecyclohexanone, an ‘ A ’ ring model for 1α, 25-dihydroxyvitamin D 3

A concise synthesis of (±)-trans-3,5-bis(t-butyldimethylsiloxy)-2-methylenecyclohexanone has been developed. The synthesis proceeds in seven steps from ethyl acetoacetate and involves a highly efficient acyl radical cyclization to construct the six-membered ring.