O. G. Volostnykh

Mass spectra of new heterocycles: IX. Main fragmentaion laws of 7-methyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)-4,5-dihydro-3H-azepine and its structural isomers (2,3-dihydropyridine, pyrrole, thiophene) under electron impact

Mass spectra were investigated for the first time of four structural isomers of heterocycles, formerly inavailable 7-methyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)-4,5-dihydro-3H-azepine, 2,2-dimethyl-6-(methylsulfanyl)-5-(1-ethoxyethoxy)-2,3-dihydropyridine, 1-isopropyl-2-(methylsulfanyl)-3-(1-ethoxyethoxy)pyrrole, and N-isopropyl-N-methyl-3-(1-ethoxyethoxy)-2-thiophenamine prepared from a single linear precursor, adduct of α-lithiated 1-(1-ethoxyethoxy)allene and isopropyl isothiocyanate. All compounds formed a molecular ion (Irel 1–6%) whose primary fragmentation at the electron impact (70 eV) occurs in two principal directions related to the cleavage of the C-O bonds in the 1-ethoxyethoxy-substituent: with a simple rupture of the bonds C-OEt and C-O(heterocycle) and with the elimination of an ethoxyethene molecule. In the spectra of 4,5-dihydro-3H-azepine and 2,3-dihydropyridine the first fragmentation channel of [M]+· dominates. The second direction prevailes at the fragmentation of pyrrole and thiophene molecular ions leading to an odd-electrons ion with m/z 171. Further fragmentation of this ion is characteristic of each isomer and resulted in the formation of diagnostic ions providing a possibility of identification of these isomers by mass spectrometry.

Mass spectra of new heterocycles: X. Fragmentation of the molecular ions of 1-alkyl(cycloalkyl, aryl)-3-alkoxy(aryl)-2-methylsulfanyl-1H-pyrroles

The mass spectra of previously unknown 1-alkyl(cycloalkyl, aryl)-3-alkoxy(aryl)-2-methylsulfanyl-1H-pyrroles were studied. Fragmentation of all 3-alkoxy-substituted pyrroles under electron impact (70 eV) follow both ether and sulfide decomposition paths; In particular, 1-R-substituted 3-methoxy-2-methylsulfanyl-1H-pyrroles (R = Me, Et, i-Pr, s-Bu, cyclo-C5H9, cyclo-C6H11, Ph) lose methyl radical group from both methoxy and methylsulfanyl groups. The mass spectra of 1-sec-butyl- and 1-cycloalkylpyrroles also contained a strong peak (10–49%) from odd-electron [M — CnH2n]+· ion formed via cleavage of the N-R bond with synchronous hydrogen transfer. Cleavage of the O-Alk bond in the fragmentation of 3-alkoxy-1-isopropyl-2-methylsulfanyl-1H-pyrroles (Alk = Et, i-Pr, t-Bu) was accompanied by rearrangement process leading to the corresponding alkene and odd-electron 1-isopropyl-2-methylsulfanyl-1H-pyrrol-3-ol ion. The main fragmentation path of 1-alkyl-2-methylsulfanyl-3-phenyl-1H-pyrroles (Alk = Me, i-Pr) under electron impact involves dissociation of the S-Me bond with formation of rearrangement 1H-[1]benzothieno[2,3-b]pyrrol-8-ium ion.

Expedient Access to Functionalized Furan/3(2H)-furanone Ensembles via Microwave-Assisted Domino Reactions

Abstract A one-pot linkage between furan and 3(2H)-furanone rings has been effected via the microwave-assisted Et3N-catalyzed domino condensation of the furan and benzofuran carboxylic acids with available cyanopropargylic alcohols (MeCN, 100 °C, 1.2 atm, 2–17 h). Despite involving a number of C-H-forming/breaking steps, the assembly is chemoselective and the final products, 5-(2-furyl)-3(2H)-furanones, are formed in 59–96% yields. GRAPHICAL ABSTRACT

Mass spectra of new heterocycles: VIII. Fragmentation of 6-alkoxy- and 6-aryl(hetaryl)-3H-azepines under electron impact

The electron impact mass spectra of previously unknown 2-alkyl-6-alkoxy-, 2,3-trimethylene-6-alkoxy- and 2-alkyl-6-aryl(hetaryl)-3H-azepines were studied. All compounds give rise to stable molecular ions (Irel = 44–100%) whose fragmentation pattern is determined mainly by the substituent on C6. Decomposition of the molecular ions derived from 6-alkoxy derivatives (R1 = MeO, EtO, i-PrO) follows general relations typical of alkyl ethers. The main characteristic peaks in the mass spectra of 2-methyl-6-aryl- and 2-methyl-6-hetaryl-3H-azepines (R1 = Ph, 1H-pyrrol-1-yl, 5-methylthiophen-2-yl) belong to even-electron rearrangement ions [M − H]+ and [M − Me]+, which have conjugated bi- and tricyclic structures, and products of their subsequent decomposition. Substituents in positions 2 (R2) and 3 (R4) [R4 = H, R2 = Me, Et; R2R4 = (CH2)3] bring some specificity to the fragmentation pattern, but their contribution is not crucial.

Heterocumulenes reactions with organometallic reagents: XV. Quantum-chemical investigatiom of skeleton rearrangements of 2-methyl-6-methoxy-3H-azepine originating from valence tautomerism

In the framework of quantum-chemical simulation (DFT) the structure was explored of six potentially probable tautomeric forms of 2-methyl-6-methoxy-3H-azepine and their relative thermodynamic stability was evaluated. In the tautomers obtained the preferred gradient channels are localized of [1,n]-H shifts capable of initiating their tautomerism. The most probable typical concerted reactions were analyzed of the formation of valence isomers, fused three-/six- and four-/five-membered carbo- and heterocycles, azabicyclo[4.1.0]hepta-2,4-dienes (azanorcaradienes) and azabicyclo[3.2.0]hepta-3,6-dienes respectively.

Reactions of heterocumulenes with organometallic reagents: XVI. Quantum-chemical study on the mechanisms of formation of homo- and heteroannular azacycloheptadienes in reactions of 2-aza-1,3,5-trienes with potassium tert-butoxide

Mechanisms of intramolecular transformations of carbanions generated from 2-aza-1,3,5-trienes by the action of potassium tert-butoxide, which could lead to homo- or heteroannular azacycloheptadienes, were studied by quantum-chemical methods in terms of the density functional theory. The corresponding gradient channels were localized for model 1-methylsulfanyl-1-(cyclopentylideneamino)- and 1-methylsulfanyl-1-(cyclohexylideneamino)buta-1,3-dien-2-ols. Analysis of the kinetic and thermodynamic parameters showed that carbanion generated from N-cyclopentylidenebuta-1,3-dien-1-amine undergoes rearrangement mainly into homoannular azacycloheptadiene and that analogous N-cyclohexylidene derivative gives rise to heteroannular isomer. The results of calculations were consistent with the experimental data.