A new approach to a vitamin D ring C/D building block from the Hajos dione, involving epoxide opening at the more substituted carbon atom

A new approach to a trans-hydrindane building block for 1α,25-dihydroxyvitamin D3 (calcitriol) synthesis from the Hajos dione has been developed. The α,β-unsaturated carbonyl group in the Hajos dione has been protected and the carbonyl group in the five-membered ring has been used for the side chain attachment. Key steps in the six-membered ring transformation include: reduction of the carbonyl group, stereoselective epoxidation of the double bond in the allylic alcohol, opening of the epoxide at the more substituted carbon atom and regioselective deoxygenation.