The synthesis of substituted phenols from pyranone precursors

The syntheses of various substituted phenols from pyranone precursors, namely 4H-pyran-4-one, 3-(benzyloxy)-2-methyl-4H-pyran-4-one (benzyl-maltol), 2,6-dimethyl-4H-pyran-4-one and diethyl 4-oxo-4H-pyran-2,6-dicarboxylate (diethyl chelidonate) are presented. A variety of pronucleophiles were used in combination with tert-butanol as solvent and potassium tert-butoxide as base, using conventional heating methods and microwave conditions.     

Application of ortho-chloro-β-aroylthioamides in synthesis(II): an efficient one-pot, three-component synthesis of tricyclic thiochromeno[2,3-b]pyridine derivatives

Tricyclic thiochromeno[2,3-b]pyridine derivatives have been successfully synthesized in an unusual one-pot multicomponent cascade reaction from ortho-halo-β-aroylthioamides, Meldrum's acid, and aromatic aldehydes. The reaction presumably proceeds via Knoevenagel condensation-Michael addition-cyclocondensation-decarboxylation-rearrangement-intramolecular S_NAr reaction sequence. High bond forming efficiency of this reaction makes it attractive for the synthesis of thiochromeno[2,3-b]pyridine derivatives in a single step operation.     

Synthesis of hexahydrocarbazoles by cyclisation of 3-(but-3-enyl) indole derivatives

A new cyclisation of 3-(but-3-enyl) indole derivatives that produces policyclic compounds with a hexahydrocarbazole structure is described. In this reaction three stereogenic centres are generated in one step, and this process can be considered as evidence of the biogenetic relationship between anominine and tubingensin A.     

Hydroxy-α-amino acids modified by ionic liquid moieties: recoverable organocatalysts for asymmetric aldol reactions in the presence of water

New chiral ionic liquids bearing proline, serine or threonine moieties were synthesized. Compounds that contain 1-dodecylimidazolium or 4-(5-n-nonyl)-pyridinium cations and NTf₂ or PF₆ anions efficiently catalyze the asymmetric aldol reaction between aldehydes and ketones in the presence of water to generate aldols with high distereo- (up to 98:2) and enantioselectivity (up to >99% ee). 4-Hydroxyproline modified by the 4-(5-n-nonyl)-pyridinium hexafluorophosphate moiety retains its activity and selectivity over at least eight reaction cycles.     

An ionic liquid mediated one-pot synthesis of substituted thiazolidinones and benzimidazoles

An expeditious one-pot synthesis of 2,3-diaryl/2-aryl-3-heteroaryl-1,3-thiazolidin-4-ones and 1-aryl-1H,3H-thiazolo[3,4-a]benzimidazoles have been accomplished by condensing hetero/aromatic amine, 2-mercaptoacetic acid, aromatic aldehyde and 1,2-phenylenediamine, 2-mercaptoacetic acid and aromatic aldehyde, respectively, in ionic liquids, viz, 1-butyl-3-methyl-imidazolium tetrafluoroborate and 1-methoxyethyl-3-methylimidazolium trifluoroacetate.     

Effect of a carboxyl group on the chemiluminescent reaction of tris(2,2′-bipyridine)ruthenium(III) with aliphatic amines

The effect of a carboxyl group beside nitrogen of aliphatic amines on the tris(2,2′-bipyridine)ruthenium(III), Ru(bpy)₃³⁺, chemiluminescent reaction was examined. It has been shown that a carboxylate anion promotes the chemiluminescent reaction at a lower pH and then the aliphatic amines with this substituent can be sensitively detected compared with corresponding aliphatic amines without this substituent. Based on this finding, preliminary studies on simultaneous determination of 4-hydroxyproline, N-methylglycine, N-methylalanine, proline, and pipecolic acid in human serum have been performed using isocratic reversed-phase ion-pair high-performance liquid chromatography (HPLC) with electrogenerated Ru(bpy)₃³⁺ chemiluminescent detection. The detection limits (signal-to-noise ratio of 3) with the proposed method were 3.0, 12, 2.7, 4.6, and 10 nM for 4-hydroxyproline, N-methylglycine, N-methylalanine, proline, and pipecolic acid, respectively.     

A direct RP-HPLC method for the determination of furanic aldehydes and acids in honey

In this study 5-hydroxymethyl-2-furaldehyde (HMF), 2-furaldehyde, 3-furaldehyde, 2-furoic acid and 3-furoic acid are contemporarily determined in honey using a swift and direct RP-HPLC approach. The validation protocol was performed in terms of detection and quantification limits, precision (by repeatability and reproducibility), linearity and accuracy (by recovery tests); the acceptability of the precision and accuracy results was positively verified using Horwitz's model and AOAC guidelines, respectively. The method was tested on 18 honey samples of different ages, and botanical and geographical origin. HMF and 2-furaldehyde correlated highly with the age of the samples, whereas no correlation was observed with regards to 2-furaldehyde and 2-furoic acid. Hypotheses relating to the formation of minority furanic compounds are also proposed.     

Synthesis of highly stable unusual charge-separated pyridinium-, isoquinolinium-, quinolinium-, and N-methylimidazolium-tetronic acid zwitterions

A unique strategy for the synthesis of highly stable unusual charge-separated pyridinium-, isoquinolinium-, quinolinium-, and N-methylimidazolium-tetronic acid zwitterions from the reaction of pyridine, isoquinoline, quinoline, and N-methylimidazole with dialkyl acetylenedicarboxylates and 3-chlorotetronic acid in EtOH at room temperature is described.     

Application of the addition of triorganozincates to N-(tert-butanesulfinyl)imines to the enantioselective synthesis of α-amino acids

Highly enantiomerically enriched N-protected α-amino acids can be easily prepared from optically pure N-(tert-butanesulfinyl)imines by a four-step sequence involving: diastereoselective addition of a triorganozincate to the imine, removal of the sulfinyl group, benzoylation of the nitrogen atom of the obtained primary amine and oxidation of one of the substituents on the carbon atom α to the nitrogen. Using the same configuration in the sulfinyl chiral auxiliary, amino acids with the (R) or the (S) configuration can be prepared by choosing the proper combination of imine and organozincate. α,α-Disubstituted α-amino esters with high optical purity can also be prepared by the diastereoselective addition of trialkylzincates to α-imino esters.     

Heteropoly acid-catalyzed aza-Prins-cyclization: an expeditious synthesis of 4-hydroxypiperidines

4-Hydroxypiperidines are prepared in good yields and with high selectivity by means of aza-Prins-cyclization using 10 mol % phosphomolybdic acid under mild reaction conditions. This is the first report on the preparation of 4-hydroxypiperidines via aza-Prins-cyclization.