To obtain the subject compound useful for efficient vitamin D analog synthesis by chlorinating a specific cyclohexane compound with triphosgene in the presence of an organic base followed by reacting the thus produced compound with a diphenylphosphine oxide salt.

This compound of formula II (Ph is a phenyl) [e.g. 3S-(3α,5 β,Z)-2-2-2-methylene-bis (1, 1-dimethyl-ethyl)dimethyl-silyl-oxy-cyclohexylidene- ethyl-diphenylphosphine oxide] is obtained by chlorinating a compound of formula I (X1 and X2 are both H or CH2 if combined together; R1 is a protective group; R2 is fluorine, H or the like; a wavy line is a bond producing the adjacent double bond representing either E-or Z-steric configuration) with triphosgene in the presence of an organic base such as triethylamine with triphosgene to produce a compound of formula II followed by reacting the thus produced compound with a diphenylphosphine oxide salt.