Synthesis of nonsymmetrical dialkylamines on the basis of diphenylphosphinic amides

A facile method for the synthesis of nonsymmetrical dialkylamines (CnH2n+1)(2)NH (n = 1-12) using the Ph2P(O) protecting group was developed. The method includes successive transformation of monoalkylamines to primary diphenylphosphinic N-alkylamides Ph2P(O)NHR' (R' = CnH2n+1, n = 1-12) by the Todd-Atherton reaction, phase transfer N-alkylation of these compounds, and hydrolysis of the secondary amides Ph2P(O)NR'R ''. thus formed. When the (EtO)(2)P(O) and Bu2P(O) protecting groups are used, N-alkylation of primary amides is accompanied by the formation of Et-O and P-N bond cleavage products, respectively. A study of the stability of the N-alkylamides R2P(O) NHR' (R = Ph, p-MeC6H4, p-ClC6H4, Bu) under strong alkaline conditions used in the phase transfer N-alkylation showed that an increase in the electron-donating ability of substituents at both the nitrogen atom and the phosphorus atom results in a decrease in the degree of P-N bond cleavage. The primary and secondary diphenylphosphinic amides containing a beta-hydroxyethyl group at the nitrogen atom are extremely unstable under the alkaline conditions and are converted quantitatively to the diphenylphosphinic acid salt.