Vitamin D3 synthetic studies. Intramolecular Diels-Alder approaches to the CD-ring fragment

Article abstract of DOI:10.1016/0040-4020(96)00147-0

The enantiospecific synthesis of the vitamin D₃ CD ring fragment 3 is reported. Key steps are the diastereoselective allylation of a norephedrine/dihydrocitronellic acid-derived oxazolidinone, and the intramolecular Diels-Alder reaction of a sulfonyl-substituted dienyne. The analogous cycloaddition reaction of a trienylsulfone substrate is shown to give products having the incorrect stereochemistry for vitamin D3 synthesis.