Phosphonomethylation of Cyclohexene Oxides

Article abstract of DOI:10.1021/jo00079a010

The tradeoff between synthetic directness and regioselectivity during oxirane ring opening is examined for two strategies used to phosphonomethylate cyclohexene oxide and substituted cyclohexene oxides derived from quinic acid and myo-inositol.Direct phosphonomethylation of the cyclohexene oxides utilizes diisopropyl lithiomethanephosphonate ((C3H7O)2P(O)CH2Li) in combination with boron trifluoride.Another more indirect route to phosphonomethylation begins with reaction of the cyclohexene oxides with (lithiomethyl)dimesitylborane (Mes2BCH2Li).In both reactions, boron plays a key role as either a Lewis acid during opening of the oxirane (diisopropyl lithiomethanephosphonate/boron trifluoride) or as a stabilizer of an adjacent carbanion in the attacking nucleophile <(lithiomethyl)dimesitylborane>.Regioselectivies for oxirane ring opening using diisopropyl lithiomethanephosphonate/boron trifluoride can be quite modest.By contrast, oxirane ring openings employing (lithiomethyl)dimesitylborane are uniform in the high degree of regioselectivity which is achieved.Factors which might influence the observed regioselectivities during nucleophilic attack on the cyclohexene oxides are also discussed.