Methylenomycin B: new syntheses based on .beta.- and .gamma.-keto phosphonates and .gamma.-keto phosphine oxides
摘要:
Methylenomycin B has been synthesized from diethyl 2-oxobutanephosphonate (4) in three steps in 39% overall yield. Starting from diethyl 3-oxobutanephosphonate (10) and diphenyl(3-oxobutyl)phosphine oxide (13), methylenomycin B has been obtained in 34% and 27% 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% aqueous solution) with the corresponding alpha-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.
Reactions of triethyl phosphite with activated olefins
作者:R.G. Harvey
DOI:10.1016/s0040-4020(01)99048-9
日期:1966.1
Reaction of triethylphosphite with a series of α,β-unsaturated esters, ketones, aldehydes, amides and nitriles in protonating solvents proceeds smoothly to furnish β-substituted phosphonate esters. This process, termed hydrophosphinylation, is quite general in contrast to reduction and reductive dimerization, the alternative reaction pathways previously observed for dibenzoylethylene. The most active