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 p K 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.