Synthesis of the Ring D-Building Block of (24S)-24-Hydroxy Vitamin D3 from Menthol, I

Natural (—)‐menthol (4) was oxidized to the lactone 9 which was alkylated with allyl bromide to a single product 10. The latter compound was transformed into bromo epoxide 33 which was cyclized with the highly reactive copper to the desired ring D Building block 18 of (24S)‐24‐hydroxy vitamin D3. The title compound 18 was synthesized also by free‐radical cyclization of enaldehyde 40.