The present invention discloses the synthone of Formula (I), wherein R1 and R2 are the same or different and represent independently hydrogen atom or hydroxyl protecting group, and its use for preparation of 19-nor vitamin D derivatives of general Formula (IV), wherein represents single or double bond, p represents an integer 0 to 3, R1 and R2 represent independently hydrogen atom or hydroxyl protecting group, R3 represents hydrogen atom, CH3 or hydroxyl group, R4, R5 and R6 represent independen...