Chemical capture of an unprecedented oxatetramethyleneethane radical cation with a through-space electronic coupling

A photoinduced electron-transfer reaction of 2,2-dianisyl-4-isopropylidene-3,3-dimethylcyclobutanone (5) in acetonitrile containing molecular oxygen or water gave 4,4′-dimethoxybenzophenone (7) and 2,2-dianisyl-4-isopropylidene-5,5-dimethylhydrofuran-3-one (8), demonstrating the chemical capture of an unprecedented oxatetramethyleneethane-type radical cation intermediate (6⁺). A density functional theory calculation suggests through-space electronic coupling between the tetramethylallyl and joined dianisylmethyl carbonyl subunits in 6⁺.     

Intramolecular nucleophilic substitution at an sp carbon: synthesis of substituted thiazoles and imidazole-2-thiones

The nucleophilic substitution reactions of vinylic bromides with intramolecular thioamide or thiourea moieties proceed to give a series of substituted thiazoles and imidazole-2-thiones.     

分子内氮原子上亲核取代反应的理论研究

Using the -CHR-(CH2)3-NFCH3(R=H, CH3, CH2CF3, CHO, COCH3) as the computational model, the two possible intramolecular reactions, nucleophilic substitution on nitrogen and elimination reaction, were studied at the theoretical level of MP2(full)/6-31+G(d,p). The results indicate that the elimination mechanism, when the -CHR radical is more basic (R=H, CH3, CH2CF3) leading to linear products R-CH2-(CH2)3N=CH2 is preferred. In contrast, electro-withdrawing groups CHO and COCH3 on the attacking site will favor the intramolecular nucleophilic substitution of nitrogen and form 5-membered heterocyclic compounds. These theoretical predictions agree with the available experiments.     

Generation and reactions of 3-alkylidene-1-pyrazoline radical cations by photoinduced electron transfer

The behavior of the 3-alkylidene-1-pyrazoline radical cations generated by photoinduced electron transfer reactions was examined. The nitrogen-retained radical cations have been detected using laser flash photolysis. The photochemical products indicate that E/Z isomerization, intramolecular cyclization, and solvent addition (acetonitrile) occurred.     

Topologically driven tandem radical cyclization-based strategy for the synthesis of oxa- and aza-cages

Tandem radical cyclization-based strategy for the synthesis of oxa- and aza-cage compounds is described. The aryl iodides 1 and N-tosyl propargylated amine 8 lead to oxa- and aza-cages, respectively, after two tandem 5-exo-trig radical cyclizations. The alcohols 11 on reaction with ⁿBu₃SnH and AIBN give rise to the oxa-cages 14 bearing the tributyltin moiety after three tandem 5-exo-trig cyclizations. On the other hand, reaction of the propargyl ether 16 under similar conditions furnishes the oxa-cage 17 by a 5-exo-trig, 4-exo-trig, 5-exo-trig tandem radical cyclization sequence.     

A Study on Bilirubin Radical Cation Generated by One-Electron Oxidation

Introduction Bilirubin (BR) is generally regarded as a toxic compound when accumulated at an abnormally high concentration in biological tissues, and in fact a normal adult man produces about 300 mg of BR a day. However, it was proposed that the bile pigments BR and biliverdin(BV), which is the precursor of BR, may protect vitamin A and linoleie acid from oxidative destruction in the intestinal tract Further stud     

Synthesis and photoinitiated radical cyclization of allyl- and propynyloxymethyl substituted cyclopentanones to tetrahydrocyclopenta[c]furanols

Bicyclic cyclopentafuranols were formed by photoinitiated radical cyclization of allyl- and propinyloxymethyl substituted cyclopentanones with high regioselectivity. The irradiations were carried out at a wavelength of 300 nm in aprotic solvents such as benzene and acetonitrile. We could also show that reductive photoinduced electron transfer (PET) of the propynyloxymethyl substituted cyclopentanone 5 does not lead to any cyclization. The starting materials were synthesized in good yields following known procedures.     

Synthesis of 2-azabicyclo[2.1.0]pentanes by the intramolecular nucleophilic substitution of cyclopropylmagnesium carbenoids with magnesium anilide

A variety of 2-azabicyclo[2.1.0]pentanes were synthesized by the intramolecular nucleophilic substitution of cyclopropylmagnesium carbenoids with magnesium anilide. The 1-chlorocyclopropyl p-tolyl sulfoxides possessing an N-aryl-substituted aminomethyl group were prepared from dichloromethyl p-tolyl sulfoxide, α,β-unsaturated carboxylic acid esters, and anilines in four steps. The deprotonation of the amine with t-BuMgCl followed by sulfoxide/magnesium exchange of the sulfoxides with i-PrMgCl led to the generation of the cyclopropylmagnesium carbenoids possessing a magnesium anilide moiety. Subsequent intramolecular nucleophilic substitution of the cyclopropylmagnesium carbenoids occurred in a 4-exo-tet manner to give the 2-azabicyclo[2.1.0]pentanes. The optically active 2-azabicyclo[2.1.0]pentane was synthesized using a p-tolylsulfinyl group as a chiral auxiliary.     

Intramolecular photocycloaddition of β-stilbazoles tethered by silyl chains

Intramolecular (2+2) photocycloaddition of β-stilbazoles tethered by silyl chains took place with high efficiency. Complexation with dicarboxylic acid or catechol further enhanced both the efficiency and stereoselectivity.     

Significant solvent effects and unusual additions of p-chloranil in the photoinduced electron-transfer reaction of 2,2-dianisyl-4-isopropylidene-3,3-dimethylcyclobutanone

A photoinduced electron-transfer reaction of 2,2-dianisyl-4-isopropylidene-3,3-dimethylcyclobutanone (1) in benzene gave two unexpected CA-adducts, 5,5-dianisyl-4,4-dimethyl-3-[1-(4-hydroxy-2,3,5,6-tetrachlorophenyl)methylethylidene]dihydrofuran-2-one (7) and 2,2-dianisyl-4-(4-hydroxy-2,3,5,6-tetrachlorophenoxy)-4-isopropenyl-3,3-dimethylcyclobutanone (8), while the reaction in acetonitrile did not, suggesting significant solvent effects on the product distribution.     

Structural modification of unsymmetrically substituted monophthalocyanines by nucleophilic reactions

New 2-nitro-substituted phthalocyanine zinc complexes were synthesized. The nucleophilic substitution of the NO₂ group was used for the first time for the structural modification of unsymmetrically substituted monophthalocyanines. The electronic absorption spectra of phthalocyanines were studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2036–2040, September, 2005.     

Initiating radical cyclizations by H transfer from transition metals

CpCr(CO)₃H and HV(CO)₄(P-P) (where P-P is a chelating diphosphine) can be used to initiate radical cyclizations by transferring H to activated terminal olefins. CpCr(CO)₃H can catalyze reductive cyclizations, with H₂ as the ultimate reductant. Appropriate substrates can be assembled by the Morita-Baylis-Hillman reaction of methyl acrylate with an aldehyde. Six- as well as five-membered rings can be formed, and a tandem cyclization to decalin can be effected.     

Synthesis of anionic hypervalent cyclic selenenate esters: relevance to the hypervalent intermediates in nucleophilic substitution reactions at the selenium(II) center

The synthesis of a diaryl diselenide that contains 2,6‐dicarboxylic acid groups, 2,2′‐diselanediylbis(5‐tert‐butylisophthalic acid) ( 10 ), is described. Diselenide 10 undergoes intramolecular cyclization in methanol to form a cyclic selenenate ester, 5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylic acid ( 11 ). The cyclization reaction proceeds more rapidly in the presence of organic bases, such as pyridine, adenine, and 4,4′‐bipyridine, to form pyridinium 5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylate ( 14 ), adeninium 5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylate ( 15 ), and 4,4′‐bipyridiniumbis(5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylate) ( 16 ), respectively. However, 2,2′‐diselanediyldibenzoic acid ( 22 ) does not undergo cyclization under similar conditions. Structural studies on cyclic selenenate esters 14 – 16 revealed that the Se???O (COO^?) secondary distances (2.170, 2.075, and 2.176 Å) were significantly shorter than the corresponding Se???O distances (2.465, 2.472, and 2.435 Å) observed for the selenenate esters stabilized by the neutral donors (CHO, COOH, and COOEt). ¹H, ¹³C, and ⁷⁷Se NMR spectroscopy of compounds 11 and 14 – 16 reveal that the aryl protons of compound 11 and the organic cations of compounds 14 – 16 exchange between the two carboxylate groups via a hypercoordinate intermediate. The corresponding hypercoordinate intermediate ( 14 b , pyridinium selenuranide) for compound 14 was detected at low temperatures using ⁷⁷Se NMR spectroscopy. The presumed hypercoordinate intermediates in the carboxylate‐exchange reactions at the selenium(II) center for a set of model reactions were optimized using DFT‐B3LYP/6–311+g(d) calculations and their structural features compared with the X‐ray structure of anionic selenenate esters 14 – 16 .     

Synthesis of triaryls: hydroxy and amine dinaphthyl and diphenanthryl aryls by one-pot electron-transfer nucleophilic substitution reactions

A new one-pot synthetic route to achieve the preparation of hydroxy and amine binaphthyl and biphenanthryl aryls is here reported. This approach involves the reaction of 1,4-bromoiodobenzene, 4,4′-diiodobiphenyl, and 1,4- and 1,5-diiodonaphthalene with the anions of 2-naphthylamine, 2-naphthol, and 9-phenanthrylamine under irradiation in liquid ammonia. The reactions proceed to afford triaryl derivatives in moderate to good yields (∼45% of 1,4-phenylene- and 1,4-naphthylene-1,1′-dinaphthalen-2-ols as well as 1,4-phenylene-1,1′-dinaphthalen-2-amine and 10,10′-diphenanthren-9-amine). Lower yields (27%) of polyaryl derivatives are obtained by reaction of 4,4′-diiodobiphenyl with anions of 2-naphthol and 9-phenanthrylamine.     

Use of electrospray ionization mass spectrometry for the investigation of radical cation chain reactions in solution: detection of transient radical cations

Electrospray ionization mass spectrometry (ESI-MS) coupled to a microreactor is an excellent tool for the investigation of reactions in solution. Here, we report the first results of our investigations into preparatively interesting electron-transfer-initiated chain reactions in solution which proceed via radical cations as reactive intermediates. The tris(p-bromophenyl)aminium hexachloroantimonate (1)-mediated [2+2] cycloaddition of trans-anethole (2) to give 1,2-bis(4-methoxyphenyl)-3,4-dimethylcyclobutane (3) was investigated. The reaction proceeds as a radical cation chain reaction via transient intermediates 2 ⁺ and 3 ⁺ that could be detected and characterized unambiguously directly in the reacting solution by ESI-MS/MS. The identity of the intermediates was confirmed by comparison with authentic MS/MS spectra of 2 ⁺ and 3 ⁺ obtained by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). In addition, substrate and product can be monitored easily in the reacting solution by APCI-MS.Part of this work was presented at the 36th Conference of the German Society for Mass Spectrometry (DGMS).     

A study of vitamin A radical cation generated by chemical and radiolytic oxidation

Electron transfer reaction between vitamin A (1) and tris(p-bromophenyl)aminium hexachloroautimonate (2) in dichloromethane (DCM) has been investigated by means of UV-VIS absorption and ESR spectroscopy. The title radical cation formed in the reaction was characterized by a new absorption band around 600 nm and a singlet unresolved ESR spectrum with g factor of 2.0038-2.0039 and line width of 20 G. Further studies indicated that ESR pattern and parameters of the radical cation generated by 7-irradiation of 1 in CFCl3 matrix at 77 K are consistent with that resulted in the chemical oxidation in DCM at ambient temperature.     

A theoretical study on the hyperfine coupling constant of the radical cations of aliphatic ethers

Summary The hyperfine coupling constants of the radical cations of dimethylether, oxetane (oxacyclobutane), and tetrahydrofuran (oxacyclopentane) are studied byab-initio molecular orbital theories. The extraordinarily large hyperfine coupling constants of the protons of the ethers that have been found experimentally are analyzed to conclude that an important mechanism of the hole delocalization is the spin polarization in the H-C-O-C-H bond. It is also found that for the ethereal systems conventional molecular orbital calculations give glaringly small spin densities but the SAC-CI calculation gives remarkably improved values.     

Synthesis of cyclopropyl silyl ethers and their facile ring opening by photoinduced electron transfer as key step in radical/radical cationic cascade reactions

Various ring-fused cyclopropyl silyl ethers with an benzylic, olefinic or acetylenic side chain have been synthesized. Upon oxidative photoinduced electron transfer (PET) the cyclopropane ring opens and forms a reactive β-keto radical, which undergoes intramolecular cyclization. In some cases we observed only formation of ring opened non-cyclized products. With olefinic side chain 5-exo-trig mode of cyclization rather than 6-endo-trig mode of cyclization takes place whereas in case of acetylenic side chain we observed 6-endo cyclization.     

Theoretical study of the thermal interconversion mechanism between the norbornadiene and quadricyclane radical cations

Geometry optimizations at the UHF/6-31G^* and UMP2/6-31G^* levels of theory were performed to find the transition state in the interconversion between norbornadiene (N) and quadricyclane (Q) radical cations. Two transition structures, TS^+·₁ and TS^+·₂, were obtained which have C₁ and C₂ symmetry, respectively. Vibrational analysis at the UHF and UMP2 levels of theory and IRC calculation showed that TS^+·₁ is the true transition state connecting N^+· and Q^+·, while TS^+·₂ is a second order saddle point.