214212-12-1Relevant articles and documents
Efficient fluorination with tetrabutylammonium dihydrogen trifluoride in a novel approach toward 1-α-fluoro-25-hydroxy-vitamin D3 analogues
Barbier, Pierre,Mohr, Peter,Muller, Marc,Masciadri, Raffaello
, p. 6984 - 6989 (1998)
The known, but hardly accessible, A-ring phosphine oxide 20, a building block for 1-α-fluoro-25-hydroxy-vitamin D3, was prepared by a new route in gram amounts from (S)-(+)-carvone in 20 steps and 0.6% overall yield. Fluorine was introduced at an early stage by the completely regio-and stereoselective trans-diaxial opening of key-epoxide 5 with neat tetrabutylammonium dihydrogen trifluoride at 95 °C. The required 2-carbon chain extension of cyclohexanol 13 was accomplished in moderate yield via S(N)' substitution with cesium phenylselanyl acetate followed by Ireland- Claisen rearrangement of the resulting ester 15. Spontaneous elimination of the derived phenyl selenoxide led stereorandomly to a 1:1 mixture of dienoates E/Z-17, which was transformed into 20 as previously described.
