Synthesis of (±)-Rosaprostol

A total synthesis of racemic rosaprostol, an untiulcer drug, has been achieved in seven synthetic steps and in 42% overall yield starting from dimethyl methanephosphonate. The key steps include intramolecular carbenoid cyclization of dimethyl 1-diazo-2-oxoundecanephosphonate 4 leading to 2-dimethoxyphosphoryl-3-hexylcyclopentanone 5 and the Horner−Wittig reaction of the latter with methyl 5-formylpentanecarboxylate 6 employed for the introduction of the methoxycarbonylhexyl moiety at C(2) of the cyclopentanone ring.