γ-Lactonizations of 2H-chromenes via cyclopropanation

A two-step synthesis of tetrahydro-2H-furochromenones from 2H-chromenes is reported. The reaction of a series of tert-butyl 2-diazoacetate derivatives with 2H-chromenes, catalyzed by Rh₂(OAc)₄, generated cyclopropane intermediates that rearranged to γ-lactones on treatment with Sn(OTf)₂.     

Synthesis of 2-aryl-2H-[1,2,4]triazoloquinolin-3-one and 2-aryl-2H-[1,2,4]triazoloisoquinolin-3-one derivatives from α-chloroformylarylhydrazines hydrochloride

The reaction of α-chloroformylarylhydrazines hydrochloride with quinoline under air provided the corresponding 2-aryl-2H-[1,2,4]triazoloquinolin-3-ones 3a-3d in 33-42% yields and unexpected isomeric 2-aryl-2H-[1,2,4]triazoloisoquinolin-3-ones 4a-4d in 30-42% yields. These two isomers were isolated and fully characterized by spectroscopic methods including X-ray crystallography. By employing 3-methylquinoline as the starting material under the same condition, the reaction only gave compound 3e-3h as sole products in 70-82% yields without the formation of isomers. A plausible mechanism was proposed through electrophilic aromatic reaction, the tandem ring cyclization and ring-opening, and oxidation for the generation of 2-aryl-2H-[1,2,4]triazoloisoquinolin-3-ones (4).     

Regioselective synthesis of polysubstituted 4H-thiopyrans from β-oxodithioesters

A simple and efficient method for the synthesis of polyfunctionalized 4H-thiopyrans by highly regioselective cyclocondensation of β-oxodithioesters with 1,1,3-trialkyl or aryl substituted prop-2-yn-1-ols using BF₃·Et₂O as the catalyst is described.     

A concise synthesis of highly functionalized α,β-unsaturated γ-butyrolactones through ring contraction of 2H-pyran-2-ones

2-Oxo-5-(1-arylvinyl)-4-piperidin-1-yl-2,5-dihydrofuran-3-carbonitriles 3 have been synthesized through ring contraction of suitably functionalized 2H -pyran-2-ones 1 by a carbanion generated in situ from nitromethane 2 in good yield. In some cases their counterpart tautomers 2-oxo-5-(1-arylethylidene)-4-piperidin-1-yl-2,5-dihydrofuran-3-carbonitriles 4 have also been isolated and characterized as minor products.     

Rhodium-catalyzed cyclopropanations of 2-aryl-2H-chromenes with dialkyl malonate esters. A comparison of α-diazo derivatives and phenyliodonium ylides

Rhodium-catalyzed reactions of 2-aryl-substituted 2H-chromenes with α-diazo esters prepared from dimethyl and tert-butyl methyl malonates were investigated, and the results were compared with reactions carried out with phenyliodonium ylides prepared from the same esters. The phenyliodonium ylide prepared from dimethyl malonate was found to give superior yields of cyclopropane products compared to the corresponding α-diazo equivalent. However, this result was reversed with tert-butyl methyl malonate when Rh₂(S-TBSP)₄ was used to decompose the diazo compound. All reactions gave 1,1-cyclopropane diesters as single diastereomers.     

Synthesis of 9-oxiranyl-9H-purine derivatives in β-cyclodextrin cavity

An efficient and mild method has been developed for the preparation of 9-oxiranyl-9H-purine derivatives. This reaction proceeds smoothly in β-cyclodextrin cavity at room temperature, giving good to excellent yields.     

One-pot synthesis of 2,3,5-substituted 1H-pyrroles via the reaction of terminal acetylenes with nitriles and EtAlCl2 catalyzed by Сp2TiCl2

A new one pot method for the synthesis of 2,3,5-substituted 1H-pyrroles in moderate to good yields (58–77%) based on multicomponent reaction of terminal acetylenes with nitriles and EtAlCl₂ in the presence of Сp₂TiCl₂ catalyst and metallic magnesium has been developed. The possible mechanistic pathway to substituted pyrroles is discussed.     

A tandem hetero Diels–Alder/Mannich approach for the synthesis of a versatile hexahydro-2H-pyrano[3,2-c]pyridin-4(3H)-one core

The synthesis of a highly functionalizable hexahydro-2H-pyrano[3,2-c]pyridin-4(3H)-one core is described and sequentially involves a hetero-Diels Alder (HDA) reaction and an intramolecular Mannich reaction resulting in selective formation of the trans-fused ring geometry.     

Oxidative ring opening of 3-hydroxyquinoline-2,4(1H,3H)-diones into N-(α-ketoacyl)anthranilic acids

N-(α-Ketoacyl)anthranilic acids were prepared by oxidative ring opening of 3-hydroxyquinoline-2,4(1H,3H)-diones by using paraperiodic acid (H₅IO₆) or sodium periodate (NaIO₄). The optimisation of the reaction conditions is described as well as the utilisation of N-(α-ketoacyl)anthranilic acids in the preparation of anthranilic acid hydrochlorides.     

Four-component synthesis of alkyl [2-[(cyclohexylamino)carbonyl]-4-oxo-2H-chromen-3(4H)-ylidene]methyl 3,4,5,6-tetrahalophthalates via a domino O-acylation/α-addition cyclization/alcoholysis sequence

A novel protocol was developed for the synthesis of alkyl [2-[(cyclohexylamino)carbonyl]-4-oxo-2H-chromen-3(4H)-ylidene]methyl 3,4,5,6-tetrahalophthalate derivatives via the one-pot, four-component domino O-acylation/α-addition cyclization/alcoholysis reaction of tetrahalophthalic anhydrides, 3-formylchromones, cyclohexyl isocyanide and various alcohols. The highlights of this novel cascade reaction include mild reaction conditions, easy workup, and high bond efficiency resulting in the formation of four new bonds (two CO, one CO and one CC) in a single operation.     

One-pot heterocyclic ring closure of 1,1′-bi-2-naphthol to 7H-dibenzo[c,g]carbazole

An operationally simple ring closure of racemic 1,1′-bi-2-naphthol (BINOL) yielded the heterocyclic aromatic compound 7H-dibenzo[c,g]carbazole (DBC). This one-pot method gave a good conversion and is suitable for gram-scale synthesis. DBC derivatives have high thermal durability, amorphous and crystalline structures with unique morphological properties, and semi-conducting behavior with potential applications in organic electronics.     

α-Dimethylaminomethylenation-induced Houben-Hoesch-type cyclization of cyanoacetanilides: a practical synthesis of 3-formyl-4-hydroxyquinolin-2(1H)-ones

The tandem reaction of cyanoacetanilides with triflic anhydride in DMF proceeded at room temperature to afford 3-formyl-4-hydroxyquinolin-2(1H)-ones in good to high yields. A detailed mechanistic study revealed that the tandem reaction proceeded via α-dimethylaminomethylenation, which promoted the subsequent Houben-Hoesch-type cyclization. Both α-functionalization and the cyclization steps were optimized, and a multi-gram scale synthesis of 3-formyl-4-hydroxyquinolin-2(1H)-one was achieved.     

A facile synthesis of 3-hydroxy-3-(trifluoromethyl)-1H-pyrrol-2(3H)-ones with Brønsted acid-catalyzed condensation–cyclization reactions of β-enamino esters and ethyl trifluoropyruvate

A facile synthesis of 3-hydroxy-3-(trifluoromethyl)-1H-pyrrol-2(3H)-ones based on trifluoroacetic acid-catalyzed condensation–cyclization reactions of β-enamino esters and ethyl trifluoropyruvate is described. These reactions afford a series of α-trifluoromethylated γ-lactam compounds in good to excellent yields under mild conditions. A preliminary trial of an asymmetric catalytic version with chiral BINOL-derived phosphoric acid as enantioselective catalyst was conducted and showed promising enantioselectivity of the desired product.     

A facile and efficient synthesis of fully substituted pyridin-2(1H)-ones from α-oxoketene-S,S-acetals

A facile and efficient synthesis of fully substituted pyridin-2(1H)-ones has been developed by the reaction of readily available α-oxoketene-S,S-acetals with malononitrile in the presence of sodium methoxide in methanol under reflux.     

An expedient route to highly functionalized 2H-chromene-2-thiones via ring annulation of β-oxodithioesters catalyzed by InCl3 under solvent-free conditions

A convenient and one-pot synthesis of 3-aroyl/heteroaroyl-2H-chromene-2-thiones and benzo[f]2H-chromene-2-thiones has been developed by the condensation of β-oxodithioesters and salicylaldehydes/α-hydroxynaphthaldehydes in the presence of indium trichloride under solvent-free conditions. The reaction is operationally facile, readily scalable, and offers rapid entry into differentially substituted chromene-2-thione scaffolds.     

Regioselective dehydrative intramolecular heteroannulation of β-allyl-β-hydroxy dithioesters: facile and straightforward entry to 2H-thiopyrans

β-Allyl-β-hydroxy dithioesters have been employed in the synthesis of hitherto unreported and synthetically demanding 2H-thiopyrans via regioselective intramolecular annulation strategy. Lewis acid BF₃·Et₂O efficiently mediates the regioselective dehydration followed by intramolecular thioannulation at room temperature. The attractive features of this protocol include mild conditions, high atom-economy and excellent yields with the elimination of water as the only by-product.     

Tandem supramolecular synthesis of substituted 2-aryl-2,3-dihydroquinazolin-4(1H)-ones in the presence of β-cyclodextrin in water

Substituted 2-aryl-2,3-dihydroquinazolin-4(1H)-ones were prepared for the first time in water under neutral conditions by the reaction of aniline, isatoic anhydride, and aldehyde mediated by β-cyclodextrin in good yields. β-Cyclodextrin can be recovered and reused with a little loss of catalytic activity.     

Unexpected formation of new chiral 3-amino-5-alkyl-2,5-dihydro-1H-pyrrolin-2-ones from N-Boc-α-amino esters

We describe a one-pot process involving the DiBAl-H reduction of the ester moiety of N-protected α-amino esters, followed by Horner-Wadsworth-Emmons olefination in the presence of the trimethyl ester phosphonoglycinate carbanion allowing the formation of new chiral 3-amino-5-alkyl-2,5-dihydro-1H pyrrolin-2-one 5. The Z-enoate 4b, which is formed during this reaction, could be converted into the corresponding lactam 5b under UV irradiation with the presence of BuLi.     

Synthesis of multisubstituted 1H-pyrrole: selenium-catalyzed reaction of γ-nitro substituted carbonyl compounds and carbon monoxide

The novel and efficient selenium-catalyzed reductive N-heterocyclization of γ-nitro substituted carbonyl compounds with carbon monoxide has been developed. Various multisubstituted 1H-pyrroles can be easily prepared by this protocol. The one-pot synthesis of ethyl 1H-pyrrole-3-carboxylate derivatives was also successfully attained by the selenium-catalyzed reaction of β-ketoester, vinyl nitro compounds and carbon monoxide.     

Oxidation of thiazolo[3,2-a]pyrimidin-3(2H)-ones with DMSO and Lawesson’s reagent

2,2′-Dimers with a central double bond were prepared by the oxidation of 5,6-disubstituted 7-methyl-5H-[1,3]thiazolo[3,2-a]pyrimidin-3(2H)-ones with DMSO and Lawesson’s reagent at room temperature. The role of DMSO as an oxidizing reagent was confirmed by NMR spectroscopy. The E-configuration of the central CC bond for the two diastereomers of compound 8m was proven by single crystal X-ray data. The dimeric thiazolopyrimidines were orange or red colored and absorption bands at 283–330 and 459–476?nm were observed in the UV spectra.