Synthesis of new proazaphosphatranes and their application in organic synthesis

We report herein the synthesis of the new proazaphosphatrane strong bases P(RNCH2CH2)3N (R=Me3CCH2, Me2CHCH2) and (1g). The new azaphosphatranes [HP(RNCH2CH2)3N]Cl (R=Me3CCH2, Me2CHCH2) have P–Nax distances of 2.047 and 1.958 Å, respectively. We also report the synthesis of the tetramine precursor proazaphosphatrane 1g [namely, (H2NCH2CH2)2NCH2CH2NH-i-Pr] in 41% yield and the use of a complexation–extraction technique to separate it from a mixture containing the di- and tri-isopropyl substituted analogs. Using a 31P NMR technique, we report the pKa value for 1gH+ (34.49). The catalytic properties of three bases P(RNCH2CH2)3N (R=i-Pr, Piv, i-Bu) are compared in the synthesis of several β-hydroxy nitriles, β-nitroalkanols, α,β-unsaturated esters and for the Michael addition of allyl alcohol to α,β-unsaturated ketones.