Enantioselective synthesis of a key A-ring intermediate for the preparation of 1α-fluoro vitamin D3 analogues

1 alpha-Fluoro A-ring dienol 2, a useful building block for the preparation of fluorinated vitamin D-3 analogues, was synthesized in eight steps from 4-{[tert-butyldimethylsilyl]oxy}-cyclohexanone. The most distinctive synthetic development to emerge from this new synthesis is an unprecedented substrate-controlled diastereoselective fluorodesilylation of an advanced dienylsilane intermediate. This is the first enantioselective route to compound 2 relying on the use of an electrophilic fluorinating reagent.