Process for the preparation of 1-hydroxylated vitamin D compounds

A process for the 1.alpha.-hydroxylation of vitamin D compounds by SE.sup.IV oxidation which comprises the oxidation of a 1-unsubstituted 5,6-trans vitamin D compound of formula I:

• ##STR7## wherein Y represents a hydrogen atom, a hydroxyl group, an alkanoyloxy group having 1 to 6 carbon atoms, an aroyloxy group having 7 to 15 carbon atoms, a lower alkoxy group having 1 to 6 carbon atoms which may be interrupted by an oxygen atom, a tetrahydropyranyloxy group or a trihydrocarbylsilyloxy group and R represents a group of the formula:- ##STR8## wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.5 which may be the same or different, each represents a hydrogen or halogen atom, a hydroxy group, an alkanoyloxy group having 1 to 6 carbon atoms, an aroyloxy group having 7 to 15 carbon atoms, a lower alkoxy group having 1 to 6 carbon atoms which may be interrupted by an oxygen atom, a tetrahydropyranyloxy group or a trihydrocarbylsilyloxy group, or R.sup.1 and R.sup.2 may together form a carbon-carbon bond or an epoxy group;
• R.sup.4 represents a hydrogen or halogen atom or a methyl or ethyl group, or R.sup.3 and R.sup.4 together represent a keto or protected keto group;
• and R.sup.6 represents a hydroxy or hydrocarbylsulphonyloxy group in the presence of a selenous acid at a pH in the range 3-9.