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Synlett 2000; 2000(5): 752
DOI: 10.1055/s-2000-6634
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Phosphazene Bases

Olivier Legrand*
  • *Institut für Organische Chemie, Universität Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland
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Publication History

Publication Date:
31 December 2000 (online)

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Phosphazene bases belong to a family of new strong non-ionic bases mainly developed by Schwesinger in the early of 1980s. Compared to other well-known nitrogen non-ionic bases such as DBN, DBU or highly hindered guanidine as PMG, the phosphazene bases are even more water stable and basic; their pKa ranging from 26 to 42, and less nucleophilic. Phosphazene bases have been first applied in alkylation of enolates with various halides. Unlike anionic bases, they are able to form a "naked" enolate which could be trapped by halides with better yields and diastereoselectivities. Recently, enantioselective synthesis of α-alkylated α-amino acids has been achieved in presence of BEMP and a catalytic amount of chiral salt derived from cinchonine or cinchonidine.