161118-67-8Relevant articles and documents
Synthesis of electron-rich sterically hindered P1 phosphazene bases by the staudinger reaction
Alexandrova, Anastasia V.,Masek, Tomas,Polyakova, Svetlana M.,Cisarova, Ivana,Saame, Jaan,Leito, Ivo,Lyapkalo, Ilya M.
, p. 1811 - 1823 (2013/04/10)
The synthesis of electron-rich P1 phosphazene bases with a sterically protected basic center by a Staudinger reaction is reported. The initial products of the reaction between peralkylated triaminophosphanes and bulky alkyl azides, phosphazides 1a-f, were isolated in all cases in good to quantitative yield. The structures of 1d and 1e were confirmed by single-crystal X-ray diffraction. Acidic hydrolysis of pyrrolidino-substituted phosphazide (pyrr)3PN3tBu 1d led to the quantitative formation of aminophosphonium salt (pyrr)3PNH2+· BF4- 8, a direct precursor to a Schwesinger's "building block" synthetic unit. Thermally induced denitrogenation of the phosphazides, which is the second step performed in most cases under solvent-free conditions gave P1 phosphazene bases 2a-f in moderate to excellent yields. A "one-pot" two-step synthesis of phosphazene bases from commercially available triaminophosphanes was discovered. Most of the syntheses were performed on a large laboratory scale. The basicities of the newly synthesized bases 2e and 2f were determined. X-ray crystal structures were obtained for base 2e and for protonated species 2d·HBF4, 2e·HBF4, and 2f·HOTs, which provided the crucial geometrical parameters around the basic center. A rationale for the higher basicity of the pyrrolidino- (pyrr)3P=NR than the piperidino- (pip)3P=NR phosphazenes is presented. A Staudinger reaction was successfully used for the synthesis of a number of sterically congested electron-rich P1 phosphazene bases in moderate to quantitative yield. The intermediate phosphazides were isolated and characterized in all cases; their application in the preparation of higher-order phosphazenes is described. Copyright
Novel, Very Strong, Uncharged Auxiliary Bases; Design and Synthesis of Monomeric and Polmer-Bound Triaminoiminophosphorane Bases of Broadly Varied Steric Demand
Schwesinger, Reinhard,Willaredt, Juergen,Schlemper, Helmut,Keller, Manfred,Schmitt, Dieter,Fritz, Hans
, p. 2435 - 2454 (2007/10/02)
The synthesis and properties of a number of very strong iminophosphorane bases up to an extremely high level of steric hindrance are described.They cover a range of ca. 4 pK units in basicity and a range of more than 11 orders of magnitude in their rates of methylation with methyl iodide.Most of the systems are readily prepared in up to molar quantities, conveniently recovered from their salts and are of high chemical and thermal stability.Crystal structures were determined in order to parametrize a force field, which is utilized in molecular modeling studies offering a rationalization of the observed differences in steric hindrance and basicity.Depending on the degree of steric protection of the basic center, these novel bases are proposed as unprecedented, versatile auxiliary bases in E2 eliminations and in reactions involving deprotonation in the presence of more or less strong electrophiles. - Key Words: Uncharged auxiliary bases / Triaminoiminophosphorane bases / Deprotonation / Hindered bases / Polymeric bases
