Novel, Very Strong, Uncharged Auxiliary Bases; Design and Synthesis of Monomeric and Polymer‐Bound Triaminoiminophosphorane Bases of Broadly Varied Steric Demand

Abstract

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.

Synthesis of macrocyclic cyclophane-based unusual α-amino acid derivatives

“…It is known that the phosphazene bases improve the yields of coupling product when sensitive substrates are involved by minimizing the unwanted side-reactions. In this respect, 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) 13 was used as a base in acetonitrile at 0 °C.…”

“…13 C NMR spectra were recorded on Bruker 75.4 MHz instrument. High resolution mass spectra were obtained on JEOL JMS-DX 303 GC-MS instrument.…”

Development of P-Spiro Chiral Aminophosphonium Salts as a New Class of Versatile Organic Molecular Catalyst

“…Firstly, the HN P NH moiety of the cation could function as a hydrogen bonding donor toward the anion; such secondary interaction has been documented. 7 Secondly, the treatment of salts with a very strong base generates an iminophosphorane [(RHN) 3 P NR], which is a strongly basic reagent known as the P 1 phosphazene of the Schwesinger base, 9 through the facile deprotonation of one of the nitrogen atoms. On the basis of this information, we planned to prepare essentially new chiral tetraaminophosphonium salts of type 1 HCl and 2 HCl (eq.…”

Equilibrium and kinetic study of the proton transfer reactions between nitroalkanes and strong organic bases — phosphazenes in tetrahydrofuran solvent

“…Phosphazenes developed by R. Schwesinger are nonionic, strong organic bases with low nucleophilicity and pK a ranging from 26 to 42 (Table 1) [1][2][3][4][5][6][7][8][9][10]. Our previous study reported the results obtained for the proton transfer reaction between P 1 -t-Bu phosphazene base and a series of nitroalkanes with increasing substituent masses at the reaction center [11].…”

“…Three P 1 -phosphazene bases: P 1 -t-Oct, BTPP and BEMP with different steric hindrances and pKa values were used in the experiments. Reproducibility problems with more basic phosphazenes prevented us from detailed study of deprotonation of carbon acids promoted by P 2 or P 4 -phosphazenes [1,4,16]. P 1 -Oct has very similar basicity to that of P 1 -t-Bu, used previously, but has a bulkier substituent at the imine nitrogen.…”