Calciferol and its relatives. Part 22. A direct total synthesis of vitamin D2 and vitamin D3

Abstract

Direct total syntheses are described of 3-deoxyvitamin D₂, vitamin D₂, and vitamin D₃. For the first, the lithio-derivative of (Z)-2-(2-methylenecyclohexylidene)ethyl(diphenyl)phosphine oxide and the Windaus–Grundmann ketone C₁₉H₃₂O were the reacting partners; for the second, the same ketone and the lithio-derivative of a protected form of (S)-(Z)-2-(5-hydroxy-2-methylenecyclohexylidene)ethyl(diphenyl)Phosphine oxide; and for the third, the same lithio-derivative and des-AB-cholestan-8-one. In these reactions, the original Z-allyl geometry of the phosphine oxides was completely preserved in the 5,6-double bond of the products, and the new (7,8-) double bond was formed with exclusive E-geometry.