Transition-metal-catalyzed denitrogenative transannulation: converting triazoles into other heterocyclic systems

Transition metal catalyzed denitrogenative transannulation of a triazole ring has recently received considerable attention as a new concept for the construction of diverse nitrogen-containing heterocyclic cores. This method allows a single-step synthesis of complex nitrogen heterocycles from easily available and cheap triazole precursors. In this Minireview, recent progress of the transition metal catalyzed denitrogenative transannulation of a triazole ring, which was discovered in 2007, is discussed.     

Formation enthalpies of organic oxygen-containing heterocyclic radicals

Enthalpies of formation (Δ _f H ^o) of 57 oxygen-containing heterocyclic radicals have been determined from literature values of the dissociation energies of C–H chemical bonds in appropriate molecules. Within the framework of a quantitative structure–property correlation based on the additive-group model, an analysis has been carried out of the obtained Δ _f H ^o values, the reliability of these data has been shown, and a set of values has been determined of the cyclic stress of the radicals being considered. The parameters of the additive-group method are recommended for the calculation of Δ _f H ^o for radicals of the considered class.     

Hydrogenation of oxygen-containing heterocyclic compounds on group VIII metals

The hydrogenation of a number of oxygen-containing heterocyclic compounds on Pt, Pd, and Rh blacks in the liquid phase at atmospheric pressure was investigated. The results are compared with data on H-D exchange with D₂O and are interpreted from the point of view of the theory of -complex adsorption.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.10, pp. 1332–1334, October, 1981.     

Anilinopyrylium salts. Their synthesis and conversion to other heterocyclic systems

Two methods for the preparation of anilinopyrylium salts are described. The conversion of these salts to pyrans, pyridines, and nitrobenzenes is discussed. Azepines, benzimidazoles, and benxotriazoles are readily obtained from the o-aminoanilinopyrylium salts.     

Transformation of cis-enyne-substituted oxiranes to 2-vinylfurans seven-membered cycloallenes as intermediates

Upon thermal activation the 1,2-epoxy-(Z)-3-hexen-5-ynes 5a-$\text{c}$ are transformed predominately into the 2-vinylfurans 9a-$\text{c}$/10a-$\text{c}$. A reaction mechanism is proposed which involves the formation of 7-membered cycloallenes (structure 3) as central intermediates.     

Synthesis of oxygen-containing heterocyclic compounds via α-chloro-δ-(trimethylsilyloxy)imines

Treatment of α-chloro-δ-(trimethylsilyloxy)ketimines, obtained by regiospecific alkylation of α-chloroketimines with 3-bromo-1-(trimethylsilyloxy)propane, with bases and nucleophiles leads to a variety of oxygen-containing heterocycles, including tetrahydrofurans and tetrahydropyrans.     

Derivatives of heterocyclic α-iminocarboxylic acids 2. Conversion of hydrazides of heterocyclic α-iminocarboxylic acids into condensed bicyclic systems

By the interaction of hydrazides of L-proline, L-thioproline, pipecolic acid, and tetrahydro-1,4-thiazine-3-carboxylic acid with an excess of a carbonyl compound, through a stage of hydrazone formation, the following compounds have been obtained: 2,3-substituted 1,3-diazabicyclo[3.3.0]octan-4-ones; 7,8-substituted 7-thia-1,7-diazabicyclo[3.3.0]octan-6-ones; and 8,9-substituted diazabicyclo[4.3.0]nonan-7-ones. Preferential translinkage of the rings is characteristic for these heterocycles in solutions; if the substitution is asymmetric, the E-isomers are predominant.For Communication 1 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1415–1421, October, 1993.     

Thallation-iodination studies of heterocyclic systems

The thallation-iodination of 3-carbonylindoles ( 4a-f ) results in orientation control with substitution occurring at the 4-position ( 6a-f ). Also described is the dithallation of N-methylpyrrole-2-carboxaldehyde ( 2 ).     

Twisted oxygen-containing oligosilanes--unprecedented examples of sigma-n mixed conjugated systems

Twisting the silicon backbone conformation in oxygen containing oligosilanes towards dihedral angles of 120-130 degrees either by intramolecular hydrogen bonding or incorporation into a covalently bonded ring system effectively extends the delocalization of electrons in these sigma-n mixed conjugated systems.     

Synthesis of new condensed heterocyclic systems

Two new diamines — [1,3-bis(5-phenyl-1,2,4-triazol-3-yl)-4,6-diamino]benzene and [1,3-di-(2-benzimldazolyl)-4,6-diamino]benzene — were synthesized from 4,6-dinitroisophthalic acid. Newheterocyclic systems — 3,5,9,11-tetraphenyl[benzo[1,2-a; 4,5-a]bis(1,2,4-triazolo[4,3-c]pyrimidine)] and 2,16-diphenyl[benzo[1,2-a;4,5-a']bis(pyrimido[1,6-a]benzimidazole)]—were obtained by reaction of the diamines with benzoyl chloride and subsequent cyclization.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1274–1277, September, 1977.     

Investigation of condensed heterocyclic pyrimido systems

2-Phenyl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimtdine-5,7-dione reacts with several nucleophilc reagents via a scheme involving nucleophilic addition with opening of the dioxopyrimidine ring at the C-N bond in the 7–8 positions. The reaction may serve as a method for the synthesis of some asymmetrical pyrazolyl derivatives of malonic acid.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1145–1147, August, 1971.     

Synthesis of oxygen-containing heterocyclic compounds based on the intramolecular O-H insertion and Wolff rearrangement of α-diazocarbonyl compounds

The addition products of Ti(IV)-enolate derived from β-keto α-diazo carbonyl compound to ketones or α,β-unsaturated compounds were subjected to Rh₂(OAc)₄-catalyzed and photo-induced diazo decomposition. The Rh₂(OAc)₄-catalyzed reaction afforded intramolecular O-H insertion products, while the photo-induced reaction gave Wolff rearrangement/intramolecular nucleophilic addition products. The transformations represent new approaches to tetrahydrofuran and γ-butyrolactone derivatives.     

Neutral homoaromaticity in some heterocyclic systems

[reaction: see text] Neutral homoaromaticity has been evaluated in heterocyclic systems related to the bicyclo[3.2.1]octane skeleton with replacement of CH(2) at C-2 in bicyclo[3.2.1]octa-3,6-diene with X = BH, AlH, Be, Mg, O, S, PH, NH (12); replacement of CH at C-3 in bicyclo[3.2.1]octa-3,6-dien-2-yl anion with PH, S, NH, O (13); and replacement at C-2 and C-3 with N and O (14). Stabilization energies (SE) are evaluated using density functional theory and homodesmotic equations at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level for series 12-14. Stabilization energies are compared with diamagnetic susceptibility exaltations, Lambda, CSGT-B3LYP/6-31G(d)//B3LYP/6-31G(d), and nucleus-independent chemical shifts (NICS), GIAO-B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d). Analysis of frontier orbitals and geometries, B3LYP/6-31G(d)//B3LYP/6-31G(d), and proton affinities of 2-azabicyclo[3.2.1]octa-3,6-diene, pyrrole, and related model systems, B3LYP/6-311+G(2d,2p)//B3LYP/6-31G(d), provide complementary evidence supporting the division of the substrates evaluated into antihomoaromatic (12, X = BH, AlH, and Be), nonhomoaromatic (12, X = O, S, NH, PH), and homoaromatic (13, X = S, PH, NH, O and 14 X = ON), with 12 (X = Mg) appearing as transitional between anti- and nonhomoaromatic.     

Cyanine dyes from seven-membered heterocyclic systems

The condensation of o-aminothiophenol with tetrahydroacetophenone, 2-ethylidenecyclohexanone, and 2-benzylidenecyclohexanone and also the condensation of N-methyl-o-aminothiophenol with 2-benzylidenecyclohexanone has given the bases of derivatives of benzo[b]cyclohexano[f]- and -[e]-1,4-thiazepines. From the hydrochlorides, perchlorates, and quaternary salts of these bases, cyanine dyes have been synthesized. The dyes—norcyanines—exhibit solvatochromism, which is explained by the existence of a hydrogen bond between the molecules of the dye and an alcohol.For part IV, see [3].