Andrzej, R.D., Lisa, M.G., Stanley, D.H., Marek, M.K., Liu, W., Masami, O., Roumen, R. and George, P.Y. (2002) Efficient synthesis of the A-ring phosphine oxide building block useful for 1α,25-dihydroxy-vitamin D3 and analogues. The Journal of Organic Chemistry, 67, 1580-1587.