Novel synthesis of 2-Substituted 19-norvitamin D A-ring phosphine oxide from -glucose as a building block

19-Norvitamin D A-ring phosphine oxide 5 was synthesized by a new sequence mode starting from -glucose as a chiral template. Transformation of the pyranoside ring into the A-ring carbocycle was achieved by the Pd-catalyzed Ferrier rearrangement. The phosphine oxide 5 was obtained in an 18% overall yield by this novel cost-effective method.