Novel synthesis of 1α,25-dihydroxy-19-norvitamin D from 25-hydroxyvitamin D

19-Norvitamin D analogs 3a and 3b were synthesized from 25-hydroxyvitamin D, obtained via a bioconversion method. The synthetic route features a highly regio- and stereoselective hydroboration reaction to afford 25-hydroxy-3,5-cyclopropyl-vitamin D derivatives 12 having olefin at the C1-10-position.