Synthesis of new proazaphosphatranes and their application in organic synthesis

We report herein the synthesis of the new proazaphosphatrane strong bases P(RNCH2CH2)(3)N (R=Me3CCH2, Me2CHCH2) and P(HNCH2CH2)(2)NCH2CH2N-i-Pr (1g). The new azaphosphatranes [HP(RNCH2CH2)(3)N]Cl (R=Me3CCH2, Me2CHCH2)have P-N-ax distances of 2.047 and 1.958 Angstrom, respectively. We also report the synthesis of the tetramine precursor proazaphosphatrane 1g [namely, (H2NCH2CH2)(2)NCH2CH2NH-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 P-31 NMR technique, we report the pK(a) value for 1gH(+) (34.49). The catalytic properties of three bases P(RNCH2CH2)(3)N (R=i-Pr, Piv, i-Bu) are compared in the synthesis of several beta -hydroxy nitriles, beta -nitroalkanols, alpha,beta -unsaturated esters and for the Michael addition of allyl alcohol to alpha,beta -unsaturate ketones. (C) 2001 Elsevier Science Ltd. All rights reserved.