Photochemical reaction of 1- and 2-naphthalenecarbonitrile with some methylbenzenes

1- and 2-Naphthalenecarbonitriles (1- and 2-NN) photochemically react with 1,2,4,5,-tetramethylbenzene (4) (but not with lower homologues). The products are 1,1'-(1,2-ethane-diyl)bis-(2,4,5-trimethylbenzene) (5) and 3-hydroxy-1-naphthalenecarbontrile with 1-NN and 5 and 1,2-dihydro-2-naphthalenecarbonitrile with 2-NN. The reaction involves electron transfer to the NN singlet excited state followed by proton transfer. 4-Methylbenzyl-(1-cyano-4-naphthyl)methyl ether (9) and the corresponding trimethylbenzylderivative 10, which contain donor and acceptor chromophores linked together, were prepared and found to show enhanced excimer emission but no photochemical reactivity, 1- and 2-NN react with 1-methoxy-4-methylbenzene (but not with the 3-isomer) analogously as with 4, but in this case small amounts of benzylated 1,2-dihydro-1-naphthalenecarbonitriles and 1,4-dihydro-2-naphthalenecarbonitriles are also formed. The mechanism is discussed in comparison with the corresponding reaction of 1,4-naphthalenecarbonitrile.     

Synthetic scope, computational chemistry and mechanism of a base induced 5-endo cyclization of benzyl alkynyl sulfides

We present an experimental and computational study of the reaction of aryl substituted benzyl 1-alkynyl sulfides with potassium alkoxide in acetonitrile, which produces 2-aryl 2,3-dihydrothiophenes in poor to good yields. The cyclization is most efficient with electron withdrawing groups on the aromatic ring. Evidence indicates there is rapid exchange of protons and tautomerism of the alkynyl unit prior to cyclization. Theoretical calculations were also conducted to help rationalize the base induced 5-endo cyclization of benzyl 1-propynyl sulfide (1a). The potential energy surface was calculated for the formation of 2,3-dihydrothiophene in a reaction of benzyl 1-propynyl sulfide (1a) with potassium methoxide. Geometries were optimized with CAM-B3LYP/6-311+G(d,p) in acetonitrile with the CPCM solvent model. It is significant that the benzyl propa-1,2-dien-1-yl sulfane (6) possessed a lower benzylic proton affinity than the benzyl prop-2-yn-1-yl sulfane (8) thus favoring the base induced reaction of the former. From benzyl(propa-1,2-dien-1-yl sulfane (6), 2,3-dihydrothiophene can be formed via a conjugate base that undergoes 5-endo-trig cyclization followed by a protonation step.     

Anomalous behavior in the two-step reduction of quinones in acetonitrile

The electrochemical reduction of eight quinones, 9,10-anthraquinone (1), duroquinone (2), 2,6-di-tert-butyl-1,4-benzoquinone (3), 2,6-dimethoxy-1,4-benzoquinone (4), 9,10-phenanthrenequinone (5), tetrachloro-1,2-benzoquinone (6), tetrabromo-1,2-benzoquinone (7) and 3,5-di-tert-butyl-1,2-benzoquinone (8), have been studied in acetonitrile. In every case it was found that cyclic voltammograms differed in significant ways from those expected for simple stepwise reduction of the quinone to its radical anion and dianion. The various types of deviations for the eight quinones have been cataloged and some speculation is offered concerning their origins.     

The photochemical reaction of 1,4-naphthalenedicarbonitrile with aromatic pinacols and pinacol ethers

Irradiation of 1,4-naphthalenedicarbonitrile (NDN) in deoxygenated acetonitrile in the presence of aromatic pinacols (1) leads to reduction of the former to the dihydro derivative 4 and the tetrahydro derivative 5 as well as to oxidative cleavage of the latter to yield ketones or aldehydes (3). Reaction with pinacol ethers (2) leads to product types 3, 4 and 5 as well as to 1(1-methoxybenzyl)-1,2-dihydro NDN derivatives (two diastereoisomers, 6 and 7). Only one of these adducts is formed in the reaction of NDN with benzyl methyl ether (8). The reaction involves electron transfer to singlet excited NDN and cleavage of the radical cations 1XXX and 2XXX to yield α-hydroxy and α-methoxy radicals, respectively. These react with NDN by proton transfer in the first case, and by carbon-carbon bond formation in the latter. The stereoselectivity observed in the adduct formation with 8 is explained by deprotonation of the radical cation and reaction of the corresponding radical with NDNXXX in the geminate solvent cage. The mechanism of these reactions is discussed in the light of a recent flash-photolysis study.     

Reactions of (1R,2S)-1,2-di(2-furyl)-1,2-di(3-guaiazulenyl)ethane and (1R,2S)-1,2-di(3-guaiazulenyl)-1,2-di(2-thienyl)ethane with tetracyanoethylene (TCNE) in benzene: comparative studies on the products and their spectroscopic properties

Reactions of the title meso forms, (1R,2S)-1,2-di(2-furyl)-1,2-di(3-guaiazulenyl)ethane (1) and (1R,2S)-1,2-di(3-guaiazulenyl)-1,2-di(2-thienyl)ethane (2), with a two molar amount of TCNE in benzene at 25 °C for 5 h (for 1) and 48 h (for 2) under oxygen give new compounds, 2,2,3,3-tetracyano-4-(2-furyl)-8-isopropyl-6-methyl-1,4-dihydrocyclohepta[c,d]azulene (3) and 2,2,3,3-tetracyano-8-isopropyl-6-methyl-4-(2-thienyl)-1,4-dihydrocyclohepta[c,d]azulene (4), respectively, in 74 and 21% isolated yields. Comparative studies on the above reactions as well as the spectroscopic properties of the unique products 3 and 4, possessing interesting molecular structures, are reported and, further, a plausible reaction pathway for the formation of these products is described.     

Radical cations of cyclopentadiene dimers—facets of an intriguing energy surface

The radical cations of various cyclopentadiene dimers can be generated by photoinduced electron transfer to strong electron acceptors. Nuclear spin polarization effects observed during these reactions provide insight into the radical cation structures. Three of the systems studied, endo-[4 + 2]-(1), anti-[2+2]-(2), and exo-(4+2]-dicyclopentadiene (5) give rise to unusual singly linked, delocalized radical cations, whereas the anti-[4 + 4]-dimer (3) and 1,3-bishomocubane (4) give rise to more conventional radical cations. The reactions of spiroheptadiene (9) and di(spiroheptadiene) (10) provide evidence for two different dimer radical cations, a doubly linked (D) and a singly linked (S) species. This finding supports a stepwise mechanism for the radical cation Diels-Alder reaction of 9.     

Transition-metal-free insertion of benzyl bromides into 2-(1H-benzo[d]imidazol-1-yl)benzaldehyde: One-pot switchable syntheses of benzo[4,5]imidazo[1,2-a]quinolin-5(7H)-ones and 3-arylquinolin-4-ones mediated by base

A transition-metal-free insertion of benzyl group between aldehyde and imidazole of 2-(1H-benzo[d]imidazol-1-yl)benzaldehyde was achieved for the first time. Two diverse sets of quinolin-4-one derivatives: benzo[4,5]imidazo[1,2-a]quinolin-5(7H)-ones (2) and 3-arylquinolin-4-ones (3) were synthesized based on identical starting materials 2-(1H-benzo[d]imidazol-1-yl)benzaldehydes (1) and benzyl bromides. In the preparations, two key intermediates I and II were involved and might be synthesized in situ through the reaction of an intra-Breslow intermediate with benzyl bromide via an enol attack in the presence of base or a NHC-based enamine attack in the absence of base, respectively, in which the intra-Breslow intermediate might function as a nucleophilic reagent by following two novel different pathways.     

Siliciumorganische verbindungen: LXXXVIII. Disilatranylalkane

By hydrosilylation of triethoxyvinylsilane (1), 1,5-hexadiene (10) and 3,3-dimethyl-3-sila-1,4-pentadiene (14) with triethoxysilane (2) we obtained 1,2-bis(triethoxysilyl)ethane (3), 1,6-bis(triethoxysilyl)hexane (11) and 1,5-bis(triethoxysilyl)- 3,3-dimethyl-3-silapentane (15). The reaction of 3 with triethanolamine (4), triisopropanolamine (6) and tris(1-t-butyl-ethanol)amine (8) leads to the 1,2-disilatranylethanes 5, 7 and 9. The 1,6-disilatranylhexanes 12 and 13 are formed from 11, 4 and 6 respectively, and 15 with 4 gives 3,3-dimethyl-1,5-disilatranyl-3-silapentane (16).     

Photochemical cyclodehydrogenation of Lewis acid-conjugates of azobenzenes

Irradiation of the conjugate acids of azobenzene (1a) with Lewis acids like anhydrous AlCl₃, anhydrous SnCl₄ and anhydrous FeCl₃ in 1,2-dichloroethane results in cyclodehydrogenation to benzo[c]cinnoline (2a). The formation of benzidine (3a) along with 2a suggests that the reaction is a photochemical disproportionation. The absorption spectra of the conjugate acids in 1,2-dichloroethane reveal that inversion of the n → π* and π → π* singlet state energies occurs on complexation of the azo nitrogen with the Lewis acid. Irradiation of the Lewis acid-conjugates of 2-methylazobenzene (1b), 2,2′-dimethylazobenzene (1c), 4,4′-dimethylazobenzene (1d) and 4-chloroazobenzene (1e) also results in cyclodehydrogenation.     

Photosensitized (electron transfer) carbon-carbon bond cleavage of radical cations : The diphenylmethyl system

The photosensitized (electron transfer) reaction of methyl 2,2-diphenylethyl ether (1), 1,1,2,2-tetraphenylethane (5), 2-methyl-1,1,2-triphenylpropane (6), and 2-methoxy-2-diphenylmethylnorbornane (11 endo and exo) with 1,4-dicyanobenzene (4) in acetonitrile-methanol leads to products indicating cleavage of an intermediate radical cation to give the diphenylmethyl radical and a carbocation. The diphenylmethyl radical is then reduced by the radical anion of the photosensitizer and protonated to yield diphenylmethane. The carbocation fragment reacts with methanol to yield ether and/or acetals. The effect of temperature on the efficiency of cleavage of 5 and 6 has been analyzed. The increase in efficiency observed at higher temperatures reflects an activation energy for the cleavage of the radical cations. In cases where no cleavage is observed, the activation energy for cleavage may be so high that back electron transfer from the radical anion of the pbotosensitizer is the dominant reaction. The C—C bond dissociation energies of the radical cations of 5 and 6 were estimated by analysis of the thermochemical cycle using the bond dissociation energies and the oxidation potentials of the neutral molecules and the oxidation potential of the diphenylmethyl and cumyl radicals. The direction of cleavage of the radical cation is explained in terms of the relative oxidation potentials of the two possible radicals.     

Silicon-carbon unsaturated compounds. 73. Photolysis of cis- and trans-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane in the presence of tert-butyl alcohol and acetone

Irradiation of cis-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane (1a) in the presence of tert-butyl alcohol in hexane with a low-pressure mercury lamp bearing a Vycor filter proceeded with high stereospecificity to give cis-2,3-benzo-1-tert-butoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (2a), in 33% isolated yield, together with a 15% yield of 1-[(tert-butoxy)methylphenylsilyl]-4-(methylphenylsilyl)butane (3). The photolysis of trans-1,2-dimethyl-1,2-diphenyl-1,2-disilacyclohexane (1b) with tert-butyl alcohol under the same conditions gave stereospecifically trans-2,3-benzo-1-tert-butoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (2b) in 41% isolated yield, along with a 12% yield of 3. Similar photolysis of 1a and 1b with tert-butyl alcohol-d₁ produced 2a and 2b, respectively, in addition to 1-[(tert-butoxy)(monodeuteriomethyl)(phenyl)silyl]-4-(methylphenylsilyl)butane. When 1a and 1b were photolyzed with acetone in a hexane solution, cis- and trans-2,3-benzo-1-isopropoxy-1,4-dimethyl-4-phenyl-1,4-disilacyclooct-2-ene (4a and 4b) were obtained in 25% and 23% isolated yield. In both photolyses, 1-(hydroxymethylphenylsilyl)-4-(methylphenylsilyl)butane (5) was also isolated in 4% and 5% yield, respectively. The photolysis of 1a with acetone-d₆ under the same conditions gave 4a-d₆ and 5-d₁ in 18% and 4% yields.     

Addition reactions of nucleophiles to dibenzoylacetylene

Several enamine diones have been prepared through the nucleophilic addition of different amines to dibenzoylacetylene (DBA). Thus, the reaction of aniline, piperidine, o-aminophenol and N-phenylbenzylamine with DBA gave the corresponding 1:1 adducts namely, 1,4 - diphenyl - 2 - (N - phenylamino)but - 2 - ene -1,4 - dione (1), 1,4 - diphenyl - 2 - piperidinobut - 2 - ene - 1,4 - dione (2), 2 - (N - 2 - hydroxyphenylamino)1,4 - diphenylbut - 2 -ene - 1,4 - dione (3) and 1,4 - diphenyl - 2 - (N - phenylbenzylamino)but - 2 - ene - 1,4 - dione (4). UV absorption data reveal that the adducts 1 and 3, formed from aniline and o-aminophenol, respectively, are the E-isomers, arising through a trans-mode of addition whereas the adducts 2 and 4, formed from piperidine and N-phenyl-benzylamine are the Z-isomers, formed through a cis-mode of addition.The reaction of N-phenaeylaniline with DBA gave 2,3 - dibenzoyl - 1,4 - diphenylpyrrole (5), whereas the reaction of 1,8 - diaminonaphthalene with DBA gave a mixture of products consisting of 2 - benzoyl - 2 - phenacyl -2,3 - dihydroperimidine (11) and 2 - benzoylperimidine (12). The reaction of 2-aminopyridine with DBA gave a mixture of two 1:1-adducts, 2 - (2 - imino - 1(2H) - pyridyl) - 1,4 - diphenylbut - 2 - ene - 1,4 - dione (14) and 1,4 -diphenyl - 2 - (N - 2 - pyridylamino)but - 2 - ene - 1,4 - dione (15).     

Reactions of bis(tetrazole)phenylenes. Surprising formation of vinyl compounds from alkyl halides

The reactions of 1,2-bis(tetrazol-5-yl)benzene (1), 1,3-bis(tetrazol-5-yl)benzene (2), 1,4-bis(tetrazol-5-yl)benzene (3), 1,2-(Bu₃SnN₄C)₂C₆H₄ (4), 1,3-(Bu₃SnN₄C)₂C₆H₄ (5) and 1,4-(Bu₃SnN₄C)₂C₆H₄ (6) with 1,2-dibromoethane were carried out by two different methods in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazoles. This lead to the formation of several alkyl halide derivatives, substituted at either N1 or N2 on the tetrazole ring, as well as the surprising formation of several vinyl derivatives. The crystal structures of both 1,2-[(2-vinyl)tetrazol-5-yl)]benzene (1-N,2-N′) (1b) and 1,3-bis[(2-bromoethyl)tetrazol-5-yl]benzene (2-N,2-N′) (5d) are discussed.     

Reaction of azulene with 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol in a mixed solvent of methanol and acetonitrile in the presence of hydrochloric acid: a facile one-pot synthesis and properties of new triarylethylenes possessing an azulen-1-yl group

Reaction of azulene (1) with 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol (2) in a mixed solvent of methanol and acetonitrile in the presence of 36% hydrochloric acid at 60 °C for 3 h gives 2-(azulen-1-yl)-1,1-bis[4-(dimethylamino)phenyl]ethylene (3) (8% yield), 1-(azulen-1-yl)-(E)-1,2-bis[4-(dimethylamino)phenyl]ethylene (4) (28% yield), and 1,3-bis{2,2-bis[4-(dimethylamino)phenyl]ethenyl}azulene (5) (9% yield). Besides the above products, this reaction affords 1,1-di(azulen-1-yl)-2,2-bis[4-(dimethylamino)phenyl]ethane (6) (15% yield), a meso form (1R,2S)-1,2-di(azulen-1-yl)-1,2-bis[4-(dimethylamino)phenyl]ethane (7) (6% yield), and the two enantiomeric forms (1R,2R)- and (1S,2S)-1,2-di(azulen-1-yl)-1,2-bis[4-(dimethylamino)phenyl]ethanes (8) (6% yield). Furthermore, addition reaction of 3 with 1 under the same reaction conditions as the above provides 6, in 46% yield, which upon oxidation with DDQ (=2,3-dichloro-5,6-dicyano-1,4-benzoquinone) in dichloromethane at 25 °C for 24 h yields 1,1-di(azulen-1-yl)-2,2-bis[4-(dimethylamino)phenyl]ethylene (9) in 48% yield. Interestingly, reaction of 1,1-bis[4-(dimethylamino)phenyl]-2-(3-guaiazulenyl)ethylene (11) with 1 in a mixed solvent of methanol and acetonitrile in the presence of 36% hydrochloric acid at 60 °C for 3 h gives guaiazulene (10) and 3, owing to the replacement of a guaiazulen-3-yl group by an azulen-1-yl group, in 91 and 46% yields together with 5 (19% yield) and 6 (13% yield). Similarly, reactions of 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (12) and 1,1-bis{4-[2-(dimethylamino)ethoxy]phenyl}-2-(3-guaiazulenyl)ethylene (13) with 1 under the same reaction conditions as the above provide 10, 2-(azulen-1-yl)-1,1-bis(4-methoxyphenyl)ethylene (16), and 1,3-bis[2,2-bis(4-methoxyphenyl)ethenyl]azulene (17) (93, 34, and 19% yields) from 12 and 10 and 2-(azulen-1-yl)-1,1-bis{4-[2-(dimethylamino)ethoxy]phenyl}ethylene (18) (97 and 58% yields) from 13.     

Comparison of the electrophilic and free-radical addition of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene

Ionic and photochemical reaction of chlorine (Cl₂), bromine (Br₂) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditions that would provide product distributions under controlled ionic or free-radical conditions. Product distributions for ionic reaction of Cl₂ and Br₂ with 1 are similar and suggest a weakly-bridged halonium ion species. Theoretical calculations support weakly-bridged chloronium and bromonium ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from ionic halogenation of 1 than 2 which correlates with the greater charge density on carbon-4 of halonium ions from 1. Ionic and free-radical reactions of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.     

Reactions of azulenes with 1,2-diaryl-1,2-ethanediols in methanol in the presence of hydrochloric acid: comparative studies on products, crystal structures, and spectroscopic and electrochemical properties

Although reaction of guaiazulene (1a) with 1,2-diphenyl-1,2-ethanediol (2a) in methanol in the presence of hydrochloric acid at 60 °C for 3 h under aerobic conditions gives no product, reaction of 1a with 1,2-bis(4-methoxyphenyl)-1,2-ethanediol (2b) under the same reaction conditions as 2a gives a new ethylene derivative, 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (3), in 97% yield. Similarly, reaction of methyl azulene-1-carboxylate (1b) with 2b under the same reaction conditions as 1a gives no product; however, reactions of 1-chloroazulene (1c) and the parent azulene (1d) with 2b under the same reaction conditions as 1a give 2-[3-(1-chloroazulenyl)]-1,1-bis(4-methoxyphenyl)ethylene (4) (81% yield) and 2-azulenyl-1,1-bis(4-methoxyphenyl)ethylene (5) (15% yield), respectively. Along with the above reactions, reactions of 1a with 1,2-bis(4-hydroxyphenyl)-1,2-ethanediol (2c) and 1-[4-(dimethylamino)phenyl]-2-phenyl-1,2-ethanediol (2d) under the same reaction conditions as 2b give 2-(3-guaiazulenyl)-1,1-bis(4-hydroxyphenyl)ethylene (6) (73% yield) and (Z)-2-[4-(dimethylamino)phenyl]-1-(3-guaiazulenyl)-1-phenylethylene (7) (17% yield), respectively. Comparative studies of the above reaction products and their yields, crystal structures, spectroscopic and electrochemical properties are reported and, further, a plausible reaction pathway for the formation of the products 3-7 is described.     

Synthesis and properties of tetraphenyltriafulvene

The reaction of the 1,2-diphenylcyclo propenium ion (5) with benzhydrylmagnesium bromide exclusively affords 1,2-diphenyl-3-benzhydrylcyclo propene (4), though the reaction of 5 with benzhydryllithium in the presence of lithium chloride yields no cyclopropene 4 but 1,3-diphenyl-3-benzhydryl-cyclopropene (6) via the intermediate formation of 1,2-diphenyl-3-chlorocyclopropene (7). The hydride abstraction from the cyclopropene 4 followed by deprotonation gives tetraphenyltriafulvene (2) as dark red crystals. The ¹³C NMR spectrum, as well as a bathochromic shift of the longest-wavelength absorption in the electronic spectrum with decrease in solvent polarity, indicates a considerable contribution of the dipolar structure at the ground state of 2. The cyclic voltammetry on 2 reveals that 2 can be readily oxidized to a stable cation radical and a less stable dication. The cation radical was also generated by chemical oxidation with silver tetrafluoroborate or antimony pentafluoride, and was investigated by ESR spectroscopy.     

Original formation of benzyl benzoates by TDAE strategy

We report herein an original photoinduced electron transfer reaction between an aromatic aldehyde and TDAE in the presence of chloromethyl-dimethoxybenzenes. Thus, the reaction of 1-chloromethyl-2,5-dimethoxy-3,4,6-trimethylbenzene (1), dichlorides 4 and 5 with a series of aromatic aldehydes, in the presence of TDAE and under light catalysis, gave the corresponding benzyl benzoates.     

The preparation,spectra and tautomerism of some 4(n-arylamino)-1,2-naphthoquinones

Twelve 4(N-arylamino)-1,2-naphthoquinones (1) have been prepared by the direct addition of substituted anilines to 1,2-naphthoquinone, and their spectra have been studied. In the solid and in ethanol solution the 1,2-naphthoquinone tautomer (1a) predominates, but in trifluoroacetic acid the 2-hydroxy-1,4-naphthoquinone-4-aryliminium (2a) is the major species.     

EPR studies on H-abstraction from methylbenzenes by “magic blue” reagent

After mixing a methylbenzene 4 with “magic blue” solution in F113 (CClF₂CCl₂F) containing bis{perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide 2 and perfluoro-1-nitroso-1-[1-(2-fluorosulfonyl)ethoxy]ethane 3 at room temperature, benzylic H-atom of 4 could be selectively abstracted by 2, and benzyl radical 5 thus generated was immediately trapped by 3. Based on hyper-fine splitting constants (hfsc), the structure of the spin adducts perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl benzyl nitroxides 6 derived from seven methylbenzenes have been identified. The mechanism of the H-abstraction/spin trapping process is also discussed.