Enantioselective Synthesis of A Key A-Ring Intermediate for the Preparation of 1α,25-Dihydroxyvitamin D3

A novel approach to the key A-ring α, β-unsaturated aldehyde 1, an important intermediate for the preparation of 1α,25-dihydroxyvitamin D3, has been developed. The strategy started from the inexpensive starting material (R)-carvone with an ene reaction serving as the key step toward the potential synthesis of vitamin D3 analogues bearing the modification at the C-2 position.