Catalyst free, one pot synthesis of phosphoramidates under environment friendly conditions

An efficient and mild one pot synthesis of phosphoramidates has been reported from simple azide precursors like benzyl, allyl and propargyl halides. The method is simple, metal free giving products in good to excellent yields with wide substrate scope. Benzyl halide derivatives (YC6H4CH2X: X = Cl, Br; Y = p-F, Br, NO2 & o-Cl, NO2) reacted with NaN3 and P(OR’)3 at room temperature gave the corresponding phosphoramidates in 86–96% yields, while the reaction with allyl halides (R1,R2C = CHCH2X: X = Cl, Br, R1 & R2 = H, Me) in 60–73% yields. In polar solvents like DMF, DMSO, THF, acetonitrile, methanol moderate yields were obtained (60%–67%) with incomplete substrate conversion. Yields were better in binary polar solvents and water–ethanol was found to be the optimum green solvent in which upto 96% yield was obtained within 4.5 h. It was also observed that triethylphosphite showed better reactivity than trimethylphosphite. Secondary and tertiary halides did not react at all under the optimized conditions. This is the first catalyst free method for the one pot synthesis of phosphoramidates which offers significant green advantages like avoids hazardous organic azides, use of environment friendly ethanol and water as a green reaction medium.

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