Mild Phase-transfer Conditions Research Articles

Mild electrophilic halogenation of chloropyridines using CCl4 or C2Cl6 under basic phase transfer conditions

Graphic Effective chlorination of 2,3,5,6-tetrachloropyridine to pentachloropyridine was realized under mild phase transfer conditions with carbon tetrachloride and 50% NaOH or solid K 3 PO 4 . Mechanistic study of this reaction indicated the possibility of an aromatic carbanionic intermediate. Hexachloroethane was established as a more selective electrophilic chlorination agent.

Highly stereoselective N-terminal functionalization of small peptides by chiral phase-transfer catalysis.

Virtually complete chirality transfer has been realized in the N-terminal alkylation of small, Schiff-base activated peptides under mild phase-transfer conditions, in which finely tuned chiral quaternary ammonium salts are used as catalysts. Repeated extension and alkylation of the N-terminal position can lead selectively to nonnatural oligopeptides (see picture).

Catalytic asymmetric synthesis of .ALPHA.-amino acid derivatives and peptides using chiral phase-transfer catalysts.

Structurally rigid, chiral spiro ammonium salts of type (R, R)- or (S, S)-1 derived from commercially available (R)- or (S)-1, 1′-bi-2-naphthol have been designed as new C2-symmetric chiral phase transfer catalysts and successfully applied to the highly efficient, catalytic enantioselective alkylation of tert-butyl glycinate Schiff base under mild phase transfer conditions to furnish α-alkyl-α-amino acids and α, α-dialkyl-α-amino acids with excellent enantioselectivity. These catalysts have been also utilized for the asymmetric terminal functionallization of peptides and asymmetric direct aldol reaction of glycine derivative.(Communicated by Hitosi NOZAKI, M. J. A., Sept. 12, 2003)

Design of new, chiral phase-transfer catalysts for practical, catalytic asymmetric synthesis

Structurally rigid, chiral spiro ammonium salts of type 1 derived from commercially available ( S)-binaphthol have been designed as a new C 2-symmetric chiral phase-transfer catalyst and successfully applied to the highly efficient, catalytic enantioselective alkylation of tert-butyl glycinate Schiff base under mild phase-transfer conditions to furnish α-alkyl-α-amino acids and α,α-dialkyl-α-amino acids with excellent enantioselectivity. These ammonium salts have been also utilized for the in situ generation of chiral quaternary ammonium fluorides.

Iron pentacarbonyl mediated coupling of benzyl halides to ketones under mild phase transfer conditions.

In a two-phase system (saturated aqueous calcium hydroxide, tetrabutylamnonium sulfate, dichloromethane, iron pentacarbonyl) benzyl bromides are readily carbonylated to dibenzyl ketones; α-α′ dibromoorthoxylene yields the o-quinodimethane iron tricarbonyl complex 8. It is inferred that the reactions proceed through transient generation of the tetracarbonyl ferrate dianion.

Versatile synthesis of sulphamate esters by phase-transfer methods

The syntheses of sulphamate esters of the general types R1R2NSO3R3, RNHSO3R3, and H2NSO3R3, where R3 may be aliphatic or aromatic, have been achieved in good yield by reaction of the appropriate sulphamoyl chlorides with alcohols and phenols under mild phase-transfer conditions. The present methods have led to generally higher yields, and to shorter reaction times and lower reaction temperatures than were hitherto found necessary. The prior preparation of the alkoxide has also been obviated. Some esters have been rearranged to the isomeric betaines.