The Synthesis of Chiral Hmpa Analogues

Abstract

In connection with our interest in alkoxide accelerated C–-C bond cleavage/rearrangements¹ we were intrigued by the solvent trispyrollidinophos-phoramide (TPPA) 1.² This commercially available³ material is more polar than HMPA. The well known activation of enolate and carbanion reactions by HMPA⁴ and the current interest⁵ in asymmetric catalysis suggested that chiral TPPA analogues might offer a convenient entry into a new series of chiral ligands for potential asymmetric organometallic reactions. Chiral phosphoramides of this type possess the distinct advantage over chiral crown ethers⁶ of ease of synthesis. They sufferfrom the same disadvantage: the chiral environment surrounds the cation, whereas the asymmetry of reaction intermediates usually involves the anion.