Novel rearrangement of 1H-2,3-benzoxazines to cyclic N-acyl hemiaminals: application to the synthesis of 1-arylnaphthalene skeletal congeners

The rearrangement of 1H-2,3-benzoxazine derivatives has been investigated. The reaction affords cyclic hemiaminal derivatives for their conversion to the corresponding 1-arylisobenzofurans, which can be trapped by various dienophiles to afford skeletal congeners of 1-arylnaphthalene lignans.     

Novel rearrangement of 7-(substituted aminomethyl)-6,7-dihydrooxazolo[2,3-f]purines to 7-(substituted amino)-7,8-dihydro-6H-[1,3]oxazino[2,3-f]purines

Oxazinopurines were obtained in high yield by the reaction of 8-bromotheophylline with morpholinomethyl-, piperidinomethyl- or indolinomethyl-substituted oxiranes without isolation of the intermediate oxazolo[2,3-f]purine.     

Facile synthesis of 4-phenylquinolin-2(1H)-one derivatives from N-acyl-o-aminobenzophenones

An efficient synthesis of 4-phenylquinolin-2(1H)-one derivatives has been achieved in a one-pot reaction from N-acyl-o-aminobenzophenones 1a-c (a: acyl=acetyl; b: acyl=propanoyl; c: acyl=heptanoyl) using NaH as a base. Treatment of 1 with NaH provided the quinolones 2a-c with 62-83% yields, whereas the reaction in the presence of alkyl iodide (alkyl=methyl, ethyl, n-octyl) gave the corresponding N-alkylated quinolones 3a-g in 75-95% yields. The alkylation reaction of 4-phenylquinolin-2(1H)-one 2a with alkyl halide gave a mixture of N-alkylated and O-alkylated products. Comparison of IR and NMR data of the N-alkylated and O-alkylated compounds with those of 2a-c indicated that 2a-c exist as the lactam form.     

Efficient N-arylation of pyridazin-3(2H)-ones

A variety of substituted pyridazin-3(2H)-ones are directly N-arylated in good yield using lead tetraacetate/zinc chloride in benzene or in substituted benzenes including chloro- and bromobenzene.     

Flash vacuum pyrolysis of 2,2-dioxo-1H,3H-pyrrolo[1,2-c]thiazoles and 2-vinyl-1H-pyrroles

The flash vacuum pyrolysis of new 1,1-dimethyl- and 1-methyl-1H,3H-pyrrolo[1,2-c]thiazole-2,2-dioxides gave penta-substituted 2-vinyl-1H-pyrroles via sigmatropic [1,8]-H shift of the corresponding azafulvenium methide intermediates. In some cases these 1H-pyrroles underwent rearrangement to 2-allyl-1H-pyrroles. Di-substituted 2-vinylpyrroles have also been prepared and their reactivity studied. Under FVP N-benzyl-pyrrol-2-ylpropenoates were converted into 3H-pyrrolizin-3-ones. On the other hand, microwave-assisted reaction of 1-benzyl-2-vinyl-1H-pyrrole gave a 4,5,6,7-tetrahydro-1H-indole derivative.     

Highly diastereoselective cycloaddition reactions of variously substituted 1-thia- and 1-thia-3-aza-buta-1,3-dienes. Synthesis of enantiomerically pure 5,6-dihydro-4H-[1,3]thiazines and 3,4-dihydro-2H-thiopyrans

The cycloaddition of 2- or 2,3-substituted 1-thia- and 1-thia-3-aza-4-dimethylamino-buta-1,3-dienes with various dienophiles in the presence of a Lewis acid provides a rapid and diastereoselective access to the 3,4-dihydro-2H-thiopyran and 5,6-dihydro-4H-[1,3]thiazine backbones. The generally observed trans relationship between the two newly created strereogenic centres was demonstrated to be the expression of a thermodynamic control of the reaction. The use of chiral dienophile derived from chiral oxazolidin-2-ones allowed us to prepare enantiopure 5,6-dihydro-4H-[1,3]thiazines and 3,4-dihydro-2H-thiopyrans. In the asymmetric synthetic process the chiral auxiliary removal step was best accomplished in the presence of samarium triflate in methanol.     

Isoquinolin-1(2H)-ones and 1,6-naphthyridin-5(6H)-ones by an N-acylation-SNAr sequence

A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-S_NAr reaction sequence, affords 50–86% yields when R¹ is n-alkyl but ≤30% yields when R¹ is α-branched.     

Preparation, spectroscopic properties of 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) lanthanide complexes and the supramolecular structure of [Nd2L2(NO3)6(H2O)2]·H2O

The reaction of lanthanide nitrate with 1,4-di (N,N-diisopropylacetamido)-2,3(1H,4H)-quinoxalinedione (L) yields six novel Ln(III) complexes ([Ln₂L₂(NO₃)₆(H₂O)₂]·H₂O) which are characterized by elemental analysis, thermogravimetric analysis (TGA), conductivity measurements, IR, electronic and ¹H NMR spectroscopies. A new quinoxalinedione-based ligand is used as antenna ligand to sensitize the emission of lanthanide cations. The lowest triplet state energy level of the ligand in the nitrate complex matches better to the resonance level of Eu(III) and Sm(III) than Tb(III) and Dy(III) ion. The f-f fluorescence is induced in the Eu³⁺ and Sm³⁺ complexes by exciting into the π-π* absorptions of the ligand in the UV. Furthermore, the crystal structures of a novel binuclear complex [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O has been determined by single-crystal X-ray diffraction. The binuclear [Nd₂L₂(NO₃)₆(H₂O)₂]·H₂O complex units are linked by the intermolecular hydrogen bonds and π-π interactions to form a two-dimensional (2-D) layer supramolecule.     

Indium-mediated regioselective mono-allylation of 1,5-dicarbonyl compounds and dehydrative cyclization to 2,3-dihydro-4H-pyran-4-ones and 3,4-dihydro-2H-[1,4]oxazines

An indium-mediated Barbier type mono-allylation of 1,5-dicarbonyl compounds and a subsequent acid-catalyzed dehydrative cyclization afforded 2,3-dihydro-4H-pyran-4-ones and 3,4-dihydro-2H-[1,4]oxazines.     

Reaction of N-fluoropyridinium fluoride with isonitriles and diazo compounds: a one-pot synthesis of (pyridin-2-yl)-1H-1,2,3-triazoles

Reaction of N-fluoropyridinium fluoride generated in situ with a series of isonitriles and diazo compounds led to the formation of the corresponding (pyridine-2-yl)-1H-1,2,3-triazoles in good yields (37-59%). Best outcome was consistently achieved with both aromatic isonitriles and stabilized diazo derivatives. The proposed reaction mechanism involves the intermediate formation of a highly reactive carbene species.     

Rapid access to 3-(N-substituted)-aminoquinolin-2(1H)-ones using palladium-catalyzed C-N bond coupling reaction

A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs₂CO₃ as a base.     

Anellated N-heterocyclic carbenes: 1,3-Dineopentyl-benzimidazol-2-ylidene,structural aspects of C-protonated precursor salts and an AgCl complex

Access to 1,3-dineopentyl-benzimidazol-2-ylidene (1) by deprotonation of various benzimidazolium salts was studied. [Ag(1)Cl] was prepared from the corresponding benzimidazolium chloride. X-ray crystal structure analyses of benzo-, naphtho- and quinoxalino-anellated imidazolium salts displayed neither significant changes nor systematic trends of bond lengths and angles within the five-membered ring. Consistently downfield shifts of the ¹³C¹H(2) nuclei reflect the influence of electron-withdrawing anellation.     

Synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-ones via Pd-catalyzed regioselective cross-coupling reaction and cyclization

An efficient and novel route for the synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 via palladium-catalyzed site-selective cross-coupling reaction and cyclization process was described. Reaction of 3-bromo-4-trifloxy-quinolin-2(1H)-one 3 with arylboronic acid catalyzed by PdCl₂(PPh₃)₂ afforded 3-bromo-4-aryl-quinolin-2(1H)-one 4, which then reacted with 2-ethynylaniline 5 via Pd-catalyzed Sonogashira coupling and CuI-mediated cyclization leading to the desired 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 in good yields.     

A convenient microwave-assisted desulfitative dimethylamination of the 2(1H)-pyrazinone scaffold using N,N-dimethylformamide

A convenient microwave-assisted methodology is developed for the generation of 5-chloro-3-(dimethylamino)pyrazin-2(1H)-ones. The method entails a chemoselective desulfitative removal of a phenylthioether bond upon DMF/H₂O treatment in the presence of sodium carbonate, yielding the desired compounds in 73-96%.     

N1,N3-Diacyl-3,4-dihydropyrimidin-2(1H)-ones: neutral acyl group transfer reagents

Readily available N1,N3-diacyl-3,4-dihydropyrimidin-2(1H)-ones efficiently acylate ammonia, primary and secondary amines to furnish primary, secondary and tertiary amides in good to excellent yields. The wide applicability of the procedure is demonstrated by running the reactions in a neutral medium, easy isolation of products, recycling of the innocuous by-product and chemoselectivity of the transformation.     

Synthesis of 3,4-disubstituted 2(1H)-quinolinones via intramolecular Friedel-Crafts reaction of N-arylamides of Baylis-Hillman adducts

3,4-Disubstituted 2(1H)-quinolinones were synthesized starting from the Baylis-Hillman adducts via the following sequential processes: (i) hydrolysis of the Baylis-Hillman adduct to acid, (ii) EDC coupling with anilines, (iii) H₂SO₄-assisted intramolecular Friedel-Crafts cyclization, and the final (iv) DBU-mediated isomerization.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

Novel synthesis of 2,2-dialkyl-3-dialkylamino-2,3-dihydro-1H-naphtho[2,1-b]pyrans

2,2-Dialkyl-3-dialkylamino-2,3-dihydro-1H-naphtho[2,1-b]pyrans were prepared from 2-naphthol, a secondary amine, and 3-hydroxy-2,2-dialkylpropanal in the presence of a catalytic amount of p-toluenesulfonic acid. This one-pot reaction involves retro-aldol disintegration of 3-hydroxy-2,2-dialkylpropanal followed by formation of a Mannich base intermediate from 2-naphthol, a secondary amine, and formaldehyde (retro-aldol product). This Mannich base then disproportionates into a quinone methide intermediate and the secondary amine is regenerated. It then forms an enamine intermediate with 2,2-dialkylacetaldehyde (another retro-aldol product). Finally, the quinone methide intermediate undergoes electrocyclic ring closure with enamines to produce the title compounds.     

N-Heterocyclic carbene-catalyzed hydroacylation of isatins with aldehydes: access to 3-acyloxy-1,3-dihydro-2H-indol-2-ones

The N-heterocyclic carbene-catalyzed hydroacylation of isatins with aldehydes has been described. This process offers a highly efficient and atom-ecomonical access to 3-acyloxy-1,3-dihydro-2H-indol-2-ones in good to excellent yields.