New chiral zwitterionic phosphorus heterocycles: synthesis, structure, properties and application as chiral solvating agents.

A family of new chiral zwitterionic phosphorus-containing heterocycles (zPHC) have been derived from methylene-bridged bis(imidazolines). These structures were unambiguously determined, including single-crystal XRD analysis for two compounds. The stability, acid/base and electronic properties of these dipolar phosphorus heterocycles were subsequently investigated.

A new class of organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines: synthesis, structure, pK(BH+) measurements, and properties.

A series of stable organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines, were efficiently synthesized from N,N'-dialkylthioureas and 3-hydroxy-2-butanone and their basicities were measured in acetonitrile. The derivatives with tert-alkyl groups on the imino nitrogen were found to be more basic than the tBuP(1) (pyrr) phosphazene base in acetonitrile. The origin of the high basicity of these compounds is discussed.

Determination of acid-base dissociation constants of very weak zwitterionic heterocyclic bases by capillary zone electrophoresis.

Thermodynamic acid-base dissociation (ionization) constants (pK(a)) of seven zwitterionic heterocyclic bases, first representatives of new heterocyclic family (2,3,5,7,8,9-hexahydro-1H-diimidazo[1,2-c:2',1'-f][1,3,2]diazaphosphinin-4-ium-5-olate 5-oxides), originally designed as chiral Lewis base catalysts for enantioselective reactions, were determined by capillary zone electrophoresis (CZE). The pK(a) values of the above very weak zwitterionic bases were determined from the dependence of their effective electrophoretic mobility on pH in strongly acidic background electrolytes (pH 0.85-2.

N-trimethylsilyloxyenamines as new aldehyde enolate synthons: general, efficient and diastereoselective aldol reaction with ketals and acetals.

(E)-N-trimethylsilyloxyenamines, easily accessible from aldonitrones, proved to be excellent nucleophiles in TMSOTf-induced diastereoselective aldol reaction, both with ketals and acetals, proceeding via an extended transition state and leading to a new aldol C-C-bond in the aldonitrone products, that can be readily hydrolysed to the corresponding aldehydes.

New lipophilic 2-amino-N,N'-dialkyl-4,5-dimethylimidazolium cations: synthesis, structure, properties, and outstanding thermal stability in alkaline media.

A series of new N,N'-dialkyl-4,5-dimethylimidazolium cations possessing electron-rich 2-imidazolylidene- or phosphoranylidene-amino substituents has been efficiently synthesized from common precursors, N,N'-dialkyl-4,5-dimethylimidazol-2-ylidenes. The new lipophilic salts obtained have been found to be highly stable towards strong alkali under both biphasic and homogeneous conditions. Their exceptional aqueous base resistance, which has hitherto only been seen with peralkylated polyaminophosphazenium cations, may be attributed to three factors: aromatic stabilization, efficient resonance charge delocalization, and steric protection of the exocyclic nitrogen linkage due to bulky lipophilic N-alkyl substituents.

Robust and efficient, yet uncatalyzed, synthesis of trialkylsilyl-protected cyanohydrins from ketones.

High-yielding cyanosilylation of ketones with NaCN and various chlorotrialkylsilanes in DMSO proceeds smoothly without catalysis to give silyl-protected ketone cyanohydrins. The unique role of DMSO consists in rendering naked cyanide anions that reversibly add to the C double bond O bond at the rate-determining step followed by fast trapping of the transient tertiary sodium cyanoalcoholates with chlorotrialkylsilanes or in situ generated cyanotrialkylsilanes. Preparatively, the reaction matches the best known catalytic cyanosilylation systems applying expensive Me(3)SiCN and demonstrates unprecedented efficiency in the synthesis of sterically congested trialkylsilyl-protected cyanohydrins.