Methylenomycin B: New Syntheses Based on β- and γ-Keto Phosphonates and γ-Keto Phosphine Oxides

Article abstract of DOI:10.1021/jo00003a051

Methylenomycin B has been synthesized from diethyl 2-oxobutanephosphonate (4) in three steps in 39 percent overall yield.Starting from diethyl 3-oxobutanephosphonate (10) and diphenyl(3-oxobutyl)phosphine oxide (13), methylenomycin B has been obtained in 34 percent and 27 percent overall yield, respectively.A characteristic feature of these syntheses of methylenomycin B is that the exo-methylene function is introduced via the Horner-Wittig reaction of formaldehyde (36 percent aqueous solution) with the corresponding α-phosphorylcyclopentenones 6 and 20.The latter were obtained from phosphorylated 1,4-diketones by intramolecular base-catalyzed cyclization.A brief discussion of some mechanistic aspects of the Conant reaction is also given.