Synthesis of α-(Trifluoromethyl)styrenes and 1,3-Di(trifluoromethyl)indanes via Electrophilic Activation of TMS Ethers of (Trifluoromethyl)benzyl Alcohols in Brønsted Acids.

TMS ethers of CF-benzyl alcohols (and their heterocyclic analogues) undergo elimination of TMSOH molecule with the formation of α-(trifluoromethyl)styrenes in yields of up to 90% under the action of strong Brønsted acids TfOH or HSO. Under the acidic conditions upon prolongation of the reaction, the α-(trifluoromethyl)styrenes are further dimerized into -/-1,3-di(trifluoromethyl)indanes in yields of up to 100%. Plausible reaction mechanisms of these electrophilic transformations including the intermediate formation of CF-benzyl carbocations are discussed.

Synthesis of bis-spirocyclic derivatives of 3-azabicyclo[3.1.0]hexane via cyclopropene cycloadditions to the stable azomethine ylide derived from Ruhemann's purple.

A reliable method for the synthesis of bis-spirocyclic derivatives of 3-azabicyclo[3.1.0]hexanes through the 1,3-dipolar cycloaddition (1,3-DC) reactions of cyclopropenes to the stable azomethine ylide - protonated form of Ruhemann's purple (PRP) has been developed.

Rhodium-Catalyzed Denitrogenative Diazole-Triazole Coupling toward Aza-Bridged Structures and Imidazole-Based Chelating Ligands.

1,4,8-Triazaocta-1,3,5,7-tetraenes, generated in situ by Rh(Piv)-catalyzed denitrogenative coupling of pyrazoles with 1-sulfonyl-1,2,3-triazoles, smoothly form 2,6,8-triazabicyclo[3.2.1]octa-3,6-dienes via intramolecular aza-Diels-Alder cycloaddition.

The carbene transfer to strong Lewis acids: copper is better than silver.

A new convenient approach to the synthesis of useful N-heterocyclic carbene complexes of group 13 metals was successfully developed. We demonstrate that air-stable copper(i) diaminocarbene complexes are excellent carbene transfer reagents for the synthesis of (IMes or IPr)MCl3 with high yields (M = Al, Ga). Use of this simple method allowed for the first time to obtain (IPr)AlCl3, inaccessible via a free carbene route.

TfOH-Promoted Reactions of TMS-Ethers of CF-Pentenynoles with Arenes. Synthesis of CF-Substituted Pentenynes, Indenes, and Other Carbocyclic Structures.

Trimethylsilyl ethers of 1,5-diaryl-3-(trifluoromethyl)-pent-1-en-4-yn-3-oles [Ar-C≡C-C(CF)(OSiMe)-CH═CH-Ar'] in the superacid TfOH give rise to reactive conjugated CF-allylic-propargylic cations [Ar-C≡C-C(CF)-CH═CH-Ar']. These species react with arenes in the presence of 1.5 equiv of TfOH forming regio- and stereoselectively 1,1,5-triaryl-3-(trifluoromethyl)-pent-2-en-4-ynes [Ar-C≡C-C(CF)═CH-CHAr'(Ar″)] in good yields.

Light-induced one-pot synthesis of pyrimidine derivatives from vinyl azides.

A one-pot procedure for the synthesis of tetrasubstituted dihydropyrimidine and pyrimidine derivatives from α-azidocinnamates was developed. The synthesis is based on the finding that the outcome of LED photolysis of α-azidocinnamates depends on the light wavelength employed. Blue light (455 nm) leads to the formation of 2H-azirines only, but violet light (395 nm), UV-A light (365 nm), or sunlight result in the transformation of the in situ formed 2H-azirines to 1,3-diazabicyclo[3.

Generation and NMR Study of Short-Lived and Reactive Trifluoroalkyl Carbocations of the α-Halogenothiophene Series in Brønsted Superacids: Reactions of the Cations with Arenes.

Protonation of oxygen in the side chain of the MeSiO group (followed by the elimination of MeSiOH) and protonation of the thiophene ring in 2-chloro(or bromo)-5-(1'-MeSiO-1'-trifluoromethyl-alkyl)thiophenes in Brønsted superacids (CFSOH, FSOH) gave rise to short-lived and reactive trifluoroalkyl carbocations of the thiophene series. These cations were studied by low-temperature NMR spectroscopy in the superacids, which shed light on their reactivity and reaction mechanisms. The cations may react with (hetero)aromatic π-nucleophiles in various directions, depending on their structures as well as the reaction temperature and time.

2-Azirine-2-carbonyl Azides: Preparation and Use as N-Heterocyclic Building Blocks.

2-Azirine-2-carbonyl azides, new reactive heterocyclic building blocks, were synthesized in high yield by the reaction of sodium azide with 2-azirine-2-carbonyl chlorides, generated by the Fe(II)-catalyzed isomerization of 5-chloroisoxazoles. 2-(Azidocarbonyl)-1-pyrroles, prepared by the Ni(II)-catalyzed reaction of 2-(azidocarbonyl)-2-azirines with 1,3-diketones, easily undergo the Curtius rearrangement in boiling BuOH to give Boc-protected α-aminopyrroles in high yield. Heating of 2-(azidocarbonyl)-1-pyrroles for a short time in inert solvents leads to the high-yield formation of benzo- and hetero-fused 1-pyrrolo[2,3-]pyridin-6(7)-ones, which are formed via a 6π electrocyclization involving the vicinal aryl or hetaryl substituent and the N═C bond of isocyanate, generated by the Curtius rearrangement of the azidocarbonyl group.

How Strong is Hydrogen Bonding to Amide Nitrogen?

The protonation of the carboxamide nitrogen atom is an essential part of in vivo and in vitro processes (cis-trans isomerization, amides hydrolysis etc). This phenomenon is well studied in geometrically strongly distorted amides, although there is little data concerning the protonation of undistorted amides. In the latter case, the participation of amide nitrogen in hydrogen bonding (which can be regarded as the incipient state of a proton transfer process) is less well-studied.

Isoxazole Strategy for the Synthesis of α-Aminopyrrole Derivatives.

The synthesis of methyl 5-aminopyrrole-3-carboxylates from 4-methyleneisoxazol-5-ones via "cyanide Michael addition/methylation/reductive isoxazole-pyrrole transformation" is developed. The last step occurs in a domino mode involving Mo(CO)-mediated reductive isoxazole ring-opening, Mo(CO)-catalyzed --isomerization of the enamine intermediate followed by 1,5-- cyclization. 5-Amino-1-pyrrolo-3-carboxylates react with 1,3-diketones, affording pyrrolo[1,2-]pyrimidine-7-carboxylates, and are easily converted into 2-diazo-2-pyrrole-4-carboxylates.

Synthesis of 1,2,4-Oxadiazoles by Tandem Reaction of Nitroalkenes with Arenes and Nitriles in the Superacid TfOH.

The tandem reaction of nitroalkenes with arenes and nitriles in the superacid CFSOH (TfOH) results in the formation of 1,2,4-oxadiazole derivatives in yields up to 96%. This reaction proceeds via the consequent interaction of arenes and nitriles, as nucleophiles, with intermediate cationic species derived by the protonation of nitroalkenes in TfOH. This is novel and general synthesis of 1,2,4-oxadiazoles, which are very important compounds for medicinal chemistry.

Stereo- and Regioselective 1,3-Dipolar Cycloaddition of the Stable Ninhydrin-Derived Azomethine Ylide to Cyclopropenes: Trapping of Unstable Cyclopropene Dipolarophiles.

A stereo- and regioselective 1,3-dipolar cycloaddition of the stable ninhydrin-derived azomethine ylide [2-(3,4-dihydro-2 H-pyrrolium-1-yl)-1-oxo-1 H-inden-3-olate, DHPO] to differently substituted cyclopropenes has been established. As a result, an efficient synthetic protocol was developed for the preparation of biologically relevant spiro[cyclopropa[ a]pyrrolizine-2,2'-indene] derivatives. DHPO has proved to be an effective trap for such highly reactive and unstable substrates as parent cyclopropene, 1-methylcyclopropene, 1-phenylcyclopropene, and 1-halo-2-phenylcyclopropenes.

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions.

In strong Brønsted acids (CFSOH, FSOH, DSO), (arysulfonyl)allenes (ArSO-CR=C=CRR) and (arylsulfinyl)allenes (ArSO-CR=C=CRR) undergo cyclization into the corresponding stable 1,2-oxathiolium ions, which were studied by means of NMR and DFT calculations. Quenching of solutions of these cations with low nucleophilic media, aqueous HCl, leads to their deprotonation with a stereoselective formation of (arysulfonyl)butadienes (for instance, ArSO-CR=C-C(Me)=CH, for R = R = Me, yields of 87-98%). Reactions of (arysulfonyl)allenes in the system TfOH (0.

TfOH-Promoted Reaction of 2,4-Diaryl-1,1,1-Trifluorobut-3-yn-2-oles with Arenes: Synthesis of 1,3-Diaryl-1-CF₃-Indenes and Versatility of the Reaction Mechanisms.

The TfOH-mediated reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-oles (CF₃-substituted diaryl propargyl alcohols) with arenes in CH₂Cl₂ afford 1,3-diaryl-1-CF₃-indenes in yields up to 84%. This new process for synthesis of such CF₃-indenes is complete at room temperature within one hour. The synthetic potential, scope, and limitations of this reaction were illustrated by more than 70 examples.

Reactions of 3,3,3-Trihalogeno-1-nitropropenes with Arenes in the Superacid CFSOH: Synthesis of ( Z)-3,3,3-Trihalogeno-1,2-diarylpropan-1-one Oximes and Study on the Reaction Mechanism.

3,3,3-Trihalogeno-1-nitropropenes C(Hal)CH═CH(NO) (Hal = F, Cl, Br) in reaction with arenes in the superacid CFSOH (TfOH) at room temperature in 1 h afford 3,3,3-trihalogeno-1,2-diarylpropan-1-one oximes C(Hal)CH(Ar)-C(Ar)═NOH (CHal-oximes) in yields of 23-99%. Such CHal-oximes having one ortho-substituent in the aryl ring exist as atropoisomers in solutions at room temperature. Several cationic intermediates of this reaction were studied by means of NMR and DFT calculations, which proves the detailed reaction mechanism of the formation of CHal-oximes in TfOH.

Reactions of 1,5-Diaryl-3-(trifluoromethyl)pent-1-en-4-yn-3-yl Cations with Benzene in TfOH. Synthesis of CF-"Helicopter"-Like Molecules.

Trimethylsilyl ethers of 1,5-diaryl-3-(trifluoromethyl)pent-1-en-4-yn-3-oles in superacid CFSOH (TfOH) give rise to the corresponding intermediate CF-pentenynyl cations. These species react with benzene to afford conjugated CF-pentenynes, which undergo subsequent cyclization, first, into CF-cycloheptadienes and, finally, into unusual CF-"helicopter"-like bicyclic structures.

Versatile structures of group 13 metal halide complexes with 4,4'-bipy: from 1D coordination polymers to 2D and 3D metal-organic frameworks.

A systematic structural study of complexes formed by aluminium and gallium trihalides with 4,4'-bipyridine (bipy) in 2 : 1, 1 : 1, and 1 : 2 stoichiometric ratios has been performed. Molecular structures of 11 complexes in the solid state have been determined for the first time. Complexes of 2 : 1 composition are molecular, while complexes of 1 : 1 composition form metal-organic frameworks of different kinds: an ionic 3D network (three interpenetrated lvt nets for AlCl3bipy), an ionic 2D network for AlBr3bipy and GaBr3bipy and a 1D coordination polymer in the case of GaCl3bipy.