N-Phenacylpyridinium bromides in the one-pot synthesis of 2,3-dihydrofurans

A one-pot three-component process for the synthesis of highly functionalized 2,3-dihydrofurans from 1,3-dicarbonyl compounds, aromatic aldehydes, and N-phenacylpyridinium bromides has been developed. Benzylidene 1,3-dicarbonyl compounds could be generated in situ from aromatic aldehydes and 1,3-dicarbonyl compounds and then reacted smoothly with N-phenacylpyridinium bromides to produce 2,3-dihydrofurans in moderate to good yields. Piperidine/acetonitrile is the optimal condition for this process. To increase the efficiency of this reaction, this one-pot process was also conducted solvent-free under classical heating conditions and grinding conditions.     

Triisobutylaluminum assisted reductive rearrangement of 2-ethoxy-4-alkyl-2,3-dihydrofurans

The reaction of AlBuⁱ₃ with the title compounds was investigated. The reductive rearrangement of 2-ethoxy-4-alkyl-2,3-dihydrofurans proceeds in the same way as that of the corresponding dihydropyran compounds although a complete lack of stereocontrol was observed. On the basis of the experimental results obtained, a likely mechanism for this reductive rearrangement is suggested.     

New transformations of 2-nitro-2,3-dihydrofurans to multi-functionalized dihydrofurans

A new type of transformation of 2-nitro-3-substituted-dihydrofurans to 4-formyl-2-hydroxy-3-substituted-2,3-dihydrofurans was accomplished in 63-84% yields by use of BF₃·OEt₂ in CH₂Cl₂ at −78 to 0°C.     

Synthesis and cationic polymerization of substituted 2,3-dihydrofurans

Cationic polymerization of substituted 2,3-dihydrofurans has been performed to investigate the substituent effect on the ring-opening polymerization. 2-Phenyl-2,3-dihydrofuran ( III ), 2-methoxy-5-phenyl-2,3-dihydrofuran ( V _a), and 2-ethoxy-5-phenyl-2,3-dihydrofuran ( V _b) were synthesized and polymerized with BF₃ etherate and AlCl₃ as acid catalysts. V _a and V _b ring-opening polymerized well to give the polymers with benzoyl as pendant group which were formed via cationic rearrangement during the ring-opening process, while III polymerized via simple opening of ethylenic double bond to form a polymer with the retention of tetrahydrofuran ring in the main chain. The nature of substituted cyclic vinyl ethers depending on substituents was also discussed.     

Facile domino access to chiral mono-, bi-, and tricyclic 2,3-dihydrofurans

The asymmetric domino Michael-S(N)2 reaction of various 1,3-dicarbonyl compounds to α-bromonitroalkenes is described for the first time, employing readily available cinchona-derived bifunctional thioureas as organocatalysts. The novel transformations were highly regio-, chemo-, diastereo-, and enantioselective, which simultaneously gave the chiral tricyclic 2,3-dihydrofurans, bicyclic 2,3-dihydrofurans, and tetrasubstituted 2,3-dihydrofurans with two vicinal chiral carbon centers.     

Synthesis of 2,3-dihydropyrido- and 2,3-dihydropyrimido-[1,4]diazepines from triaminopyridine and triaminopyrimidine

The reaction of 2,3,6-triaminopyridine 1 and 4,5,6-triaminopyrimidine 2 with one equivalent of the chal-cones 3, in acetic acid, leads to the formation of the 8-amino-2,3-dihydro-1H-pyrido[2,3-b][1,4]diazepine and 6-amino-2,3-dihydro-1H-pyrimido[4,5-b][1,4]diazepine derivatives 4 and 5 . The products were characterized by NMR techniques such as ¹³C, ¹H, and DEPT including selective ¹³C{¹H} decoupling experiments.     

STUDY ON CATIONIC RING-OPENING COPOLYMERIZATION OF 1,4-ANHYDRO-2,3-DI-O-BENZYL-α-D-RIBOPYRANOSE WITH 1,4-ANHYDRO-2,3-O-ISOPROPYLIDENE-α-D-RIBOPYRANOSE

Cationic ring-opening copolymerization of 1, 4-anhydro-2, 3-O-isopropylidene-α-D-ribo-pyranose (AIRP) with 1,4-anhydro-2,3-di-O-benzyl-α-D-ribopyranose (ADBR) preparedfrom D-ribose was studied. Copolymerization using SbCl_5 or BF_3 OEt_2 as catalyst atlow temperature gave stereoregular (1→4)β-D-ribofuranan (C-1 and C-4 ring cleavagesee Scheme 1) or (1→5) α-D-ribofuranan (C-1 and C-5 ring cleavage) respectively. Theeffects of catalysts, reaction time and temperatures on yield and stereoregularity of the ob-tained polymers were studied. Polymers were characterized by molecular weight, ~1HNMR,~(13)CNMR and optical rotation.     

NMR studies of the configuration of the isomeric 2,3-dimethyloxetanes

The ¹H and ¹³C NMR spectra of cis- and trans-2,3-dimethyloxetane have been re-examined and the published NMR assignments shown to be in error.     

Unexpected formation of tetrasubstituted 2,3-dihydrofurans from the reactions of beta-keto polyfluoroalkanesulfones with aldehydes

Catalyzed by piperidine, the reactions of beta-keto polyfluoroalkanesulfones with aromatic aldehydes afforded the unexpected tetrasubstituted 2,3-dihydrofurans in good yields, probably proceeding through the normal Knoevenagel condensation products. This reaction provided an efficient and novel method for the stereoselective synthesis of fluorine-containing tetrasubstituted trans-2,3-dihydrofurans.     

Easily accessible non-aromatic heterocycles with handles: 4-bromo-2,3-dihydrofurans from 1,2-dibromohomoallylic alcohols

The first general preparation of 4-bromo-2,3-dihydrofurans is reported. These non-aromatic heterocycles containing a useful coupling handle are accessed via Cu-catalyzed intramolecular cyclization of 1,2-dibromohomoallylic alcohols, which are themselves available in just two steps from aromatic and aliphatic aldehydes and ketones. Molecular dynamics simulations using the simple substrates and key geometric parameters provide a rationale for the selectivities observed. The synthetic utility of the 4-bromodihydrofurans is also demonstrated.

The first general preparation of 4-bromo-2,3-dihydrofurans is reported.     

A One‐pot Facile Synthesis of 2,3‐Dihydroxyquinoxaline and 2,3‐Dichloroquinoxaline Derivatives Using Silica Gel as an Efficient Catalyst

An efficient one‐pot reaction has been developed for the synthesis of 2,3‐dichloroquinoxaline derivatives 3a – n . The reaction was performed in two steps via a silica gel catalyzed tandem process from o‐phenylenediamine and oxalic acid, followed by addition of phosphorus oxychloride (POCl₃). A variety of 2,3‐dichloroquinoxalines have been obtained in good to excellent overall yields. Eight known compounds 3a – 3h were characterized by IR, ¹H‐NMR, and mass spectroscopies. Compounds 3i – 3n without spectroscopic data were characterized by IR, ¹H‐NMR, ¹³C‐NMR, and mass spectroscopies.     

Synthesis of 2,3‐Disubstituted 5‐Iodo‐1H‐Pyrrolo[2,3‐b]pyridines via Fischer Cyclization

A simple and convenient procedure for the preparation of some unknown 2,3‐disubstituted 5‐iodo‐1H‐pyrrolo[2,3‐b ]pyridines from readily available starting materials by Fischer indole cyclization in polyphosphoric acid is described. The present methodology provides an alternative synthetic approach to the synthesis of 5‐iodo‐7‐azaindole scaffold. All synthesized compounds were characterized by IR, MS, ¹H and ¹³C NMR, and elemental analysis.     

A Simple Efficient Procedure for the Synthesis of Benzopyrano[2,3‐c]pyrazoles

A one‐step procedure is proposed for synthesizing 2‐acyl benzopyrano[2,3‐c]pyrazoles and 2‐aryl benzopyrano[2,3‐c]pyrazoles. The method is based on the condensation of 2‐iminocoumarin‐3‐carbonitriles with hydrazides and hydrazines in acid as catalysts. A mechanism of reaction is proposed. All prepared compounds are identified by FTIR, ¹H NMR, ¹³C NMR, mass spectroscopy, and elemental analysis.     

Alkali-Induced Optical Rotation Changes in Heparins and Heparan Sulfates,and Their Relation to Iduronic Acid-Containing Sequences

Abstract

Under specific basic conditions, the glucosaminoglycans heparin and heparan sulfate, containing α-L-iduronic acid 2-O-sulfate, undergo selective epoxidation between C-2 and C-3 of this residue, with formation of a residue of 2,3-anhydro-α-L-guluronic acid. The epoxidation reaction was studied by means of ¹³C NMR and optical rotation measurements. The optical rotation values correlate well with the composition of the reaction products as determined by ¹³C NMR, thus indicating that the heparin- or heparan-like character of both natural and semisynthetic polysaccharides can be easily determined also through optical rotation measurements.     

Synthesis and antimicrobial activity of 2,4-diaryl-2,3-dihydrobenzo[b][1,4]thiazepines

A new series of structurally diverse 2,3-dihydrobenzo[b][1,4]thiazepines (2,3-dihydro-1,5-benzothiazepines) with substituted phenyl groups at C(2) and C(4) have been synthesized by reaction of 3-(5-bromo-2-methoxyphenyl)-1-arylpropen-1-ones with 2-aminobenzenethiols. The structures of all the synthesized compounds were confirmed by their analytical and spectral data (IR, ¹H NMR, ¹³C NMR). All the synthesized compounds were evaluated for antibacterial and antifungal activity against a variety of bacterial and fungal strains and interesting results were obtained. Some of the compounds had antibacterial and antifungal activity comparable to that of ciprofloxacin and fluconazole.     

Synthesis and Halogen Bonding in the Crystal Structures of the New 2,3‐Diiodo Indenone and 1‐Ethoxy‐2,3‐diiodo Indene

The CuI‐catalyzed addition of iodine to the C≡C triple bond of 3,3‐diethoxy‐1‐phenyl propyne ( 1 ) unexpectedly leads to the new cyclization products 2,3‐diiodo‐1H‐inden‐1‐one ( 2 ) and 1‐ethoxy‐2,3‐diiodo‐1H‐indene ( 3 ). Both compounds were isolated and characterized via ¹H, ¹³C NMR (Nuclear Magnetic Resonance) spectroscopy and HRMS (High Resolution Mass Spectrometry). The molecular and crystal structures of compounds 2 and 3 were determined by single crystal X‐ray diffraction. Their crystal structures are governed by extensive halogen bonding, involving I·I and I·O interactions.     

A theoretical study of inversion barriers and NMR chemical shifts of 3-pyrazolines (2,3-dihydro-1H-pyrazoles)

A rather neglected family of heterocyclic compounds, the 3-pyrazolines or 2,3-dihydro-1H-pyrazoles, has been studied theoretically at the B3LYP/6–311++G(d,p) level to obtain geometries and energies and at the GIAO/B3LYP/6–311++G(d,p) level for NMR chemical shifts. The calculated barriers of inversion of the N-substituents reproduce adequately the scarce experimental data. The calculated ¹H and ¹³C chemical shifts are consistent with those reported in the literature. A combination of both results, geometries, and ¹³C chemical shifts, shed light on the conformation of N-phenyl groups.     

Three-component reaction of triphenylphosphine,dialkyl but-2-ynedioate and arylidene pivaloylacetonitrile for diastereoselective synthesis of densely substituted 2,3-dihydrofurans

The three-component reaction of triphenylphosphine,dialkyl but-2-ynedioate and arylidene pivaloylacetonitrile in dry methylene dichloride at room temperature resulted in unexpected densely substituted 1-(triphenyl-λ~5-phosphanylidene)ethyl)-2,3-dihydrofurans in satisfactory yields with high diastereoselectivity.The relative configuration of the 2,3-dihydrofurans was elucidated by determination of single crystal structures.     

Synthesis of some pyrano[2,3‐c]pyrazoles

Synthetic methods have been developed to prepare pyrano[2,3‐c]pyrazoles with various substituents at ring positions 1, 3, and 6. The ¹H‐ and ¹³C‐NMR properties of these products and their precursors are presented and discussed. J. Heterocyclic Chem., (2011).     

Configuration and conformation of methyl 2,3-anhydro-4-deoxy-pyranosides by 1H and 13C NMR spectra

¹³C NMR spectra of 24 methyl 2,3-anhydro-4-deoxy-pento and hexopyranosides have been obtained. ¹H NMR spectra were also recorded for comparison purposes. The ¹³C NMR data can be used for differentiation of the stereo-isomeric epoxide configuration. ¹H and ¹³C NMR spectra give some insight, though still of qualitative nature, into conformation of epoxy compounds.