Synthesis of γ- and δ-lactones from 1α-hydroxy-5,6-trans-vitamin D3 by ring-closing metathesis route and their reduction with metal hydrides

New synthetic pathway towards 19-functionalized derivatives of 1α-hydroxy-5,6-trans-vitamin D3 was described. Ring-closing metathesis (RCM) of 1α-hydroxy-5,6-trans-vitamin D3 1-ω-alkenoates was a key-step. Hydride reduction of resulting lactones led to the new vitamin D3 analogues.