Synthetic Approaches to Vitamin D

This review describes the major synthetic approaches to the triene unit of vitamin D. In addition, various syntheses of two of the most important intermediates, dienoate (-)-18 and enyne (-)-32 as well as their close relatives, are presented. 1 Introduction 2. Construction of the Triene Unit of Vitamin D 2.1 Bond a Approach 2.1.1 A-ring Allylic Phosphine Oxide and CD-ring Grundmann Ketone (a) Lythgoe Approach (b) Hoffmann-La Roche Approach 2.1.2 A-ring Enyne and CD-ring Grundmann Ketone / Enol Triflate (a) Lythgoe Approach (b) Okamura Approach (c) Mouriño Approach 2.1.3 CD-ring Sulfone and A-ring Dienal (Umpolung Fashion) 2.2 Bond b Approach 2.2.1 CD-ring Methylene Sulfone and A-ring α,β- Unsaturated Ester / Aldehyde 2.2.2 Mazur Solvolysis of Cyclovitamin D₃ (a) Fukumoto and Kametani Approach (b) Wilson Approach 2.2.3 Palladium-catalyzed Cyclization and Coupling (a) Trost Approach (b) Nuss Approach 2.3 Bond c Approach 2.3.1 Lythgoe Approach 2.3.2 Takano Approach 3 Syntheses of Important A-ring Intermediates 3.1 Syntheses of Dienoate (-)-18 and Its Relatives 3.1.1 Posner Approach 3.1.2 Shimizu Approach 3.1.3 Crich Approach 3.1.4 Hoffmann-La Roche Approach 3.1.5 Kobayashi Approach 3.1.6 Takano Approach 3.2 Syntheses of Enyne (-)-32 and Its Relatives 3.2.1 Lythgoe Approach 3.2.2 Desmaele Approach 3.2.3 Hoffmann-La Roche Approach 3.2.4 Mouriño Approach 3.2.5 Okamura Approach 3.2.6 Takano Approach 4 Conclusions