The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.     

Photoinduced electron transfer reactions: Oxidation of electron-rich dioxenes and 2,3,5,6-tetraphenyl-p-dioxin induced by 2,4,4,6-tetrabromocyclohexa-2,5,-dienone

2,4,4,6-Tetrabromocyclohexa-2,5-dienone (TBCHD) sensitizes the photo-oxygenation of dioxenes and 2,3,5,6-tetraphenyl-p-dioxin by electron transfer to yield ethane-1,2-diol dibenzoates and (Z)-stilbenediol dibenzoate respectively, together with small quantities of the corresponding α-diketones. A preliminary investigation of the physical properties of TBCHD supports a radical cation chain mechanism in which the active oxygen species involved is molecular oxygen. A comparison with the photo-oxygenation of the same substrates sensitized by 9,10-dicyanoanthracene is also reported.     

Effect of Substituents,Solvent, and Temperature on the Reactivity of the Zwitterionic Peroxides Arising from the Photo-Oxygenation of 2-(Methoxymethylidene)- and 2-(Phenoxymethylidene)adamantane

The photo-oxygenation of 2-(methoxymethylidene)adamantane ( 3 ) creates a zwitterionic peroxide which may be captured by acetaldehyde to give the corresponding pair of diastereoisomeric tricyclo[3.3.1.1^3,7]decane-2-spiro-6′ -(3′ -methyl-5′ -methoxyl′, 2′, 4′ -trioxanes) ( 4 ). Ease of capture depends strongly on solvent polarity and temperature. When these are low, yields of trioxine are high (～ 80%). Conversely, 1,2-dioxetane formation is favoured at high temperature and solvent polarity. 2-(Phenoxymethylidene)adamantane ( 5 ), on photo-oxygenation, only gives the corresponding 1,2-dioxetene, even in the presence of acetaldehyde. From a Hammett, study of the-oxygenation of the enol ether 5 and p-methoxy, p-methyl, p-chloro and m-chloro derivatives, 9, 11, 13 , and ( 15 ), a good linear relation was found between substituent constants and oxygenation rates which yielded reaction constants (ρ) of 2.59, ?2.40, ?1.09, and ?0.90 in benzene, AcOET, CH₂Cl₂, and MeOH respectively. This data to the formation of a zwitterionic peroxide which enjoys stabilization from its won substituents and by competing solvation and further explains the predominance of dioxetane to the detriment of trioxane formation.     

(2σ + 4π) Photocycloaddition of 1,2-diarylcyclopropanes to 9,10-dicyanoamthracene via geminate radical ion pair

Irradiation of a degassed acetonitrile solution containing 9,10-dicyanoanthracene (DCA) and 1,2-diarylcyclopropanes gave (2σ + 4π) photocycloadducts in good yields. The geminate radical ion pairs between DCA and the cyclopropanes are involved as key intermediates in this photoreaction.     

Enantioselective addition of diethylzinc to aromatic aldehydes catalyzed by C2-symmetric chiral diols

Optically pure C₂-symmetric diols have been synthesized with moderate yields in a straightforward manner, and are used as catalysts in the enantioselective alkylation of aromatic aldehydes with diethylzinc. The addition of diethylzinc to benzaldehyde and sterically hindered 1-naphthaldehyde was achieved with excellent enantioselectivities (97–99% ee) under catalysis with (1R,2R)-1,2-bis(3,5-dibromophenyl)-ethane-1,2-diol and (1R,2R)-1,2-bis(3,5-diphenylphenyl)-ethane-1,2-diol.     

CuI/glycerol mediated stereoselective synthesis of 1,2-bis-chalcogen alkenes from terminal alkynes: synthesis of new antioxidants

(E)-1,2-Bis-chalcogen alkenes were stereoselectively prepared in good yields by the addition of diorganyl dichalcogenides to terminal alkynes using CuI/Zn/glycerol as a recyclable catalytic system. The antioxidant activity in vitro of four (E)-1,2-bis-chalcogen alkenes synthesized was evaluated and (E)-1,2-bis-(4-methoxyphenylselanyl)styrene 3b presented excellent activity. The catalytic system used in the synthesis was recovered and used directly up to 5 cycles without loss of activity.     

Bifunctional thiophosphinamide catalyzed highly enantioselective Michael addition of acetone to (E)-2-azido β-nitrostyrenes and the subsequent reductive cyclization

We have proven that primary amine/thiophosphinamide incorporating (1R,2R)-1,2-diphenylethane-1,2-diamine is an efficient catalyst for the asymmetric Michael addition of acetone to (E)-2-azido β-nitrostyrenes. Under the optimal reaction conditions, the corresponding Michael addition products were obtained in excellent yields with almost perfect stereocontrol. Upon treatment with Et₃SiH/InCl₃, the Michael addition products could be successfully converted to the related 2-methyltetrahydroquinolines in acceptable yields with moderate to excellent diastereoselectivity and without appreciable loss in optical purity. This process provides a highly enantioselective pathway for the synthesis of biologically important 2-methyltetrahydroquinoline derivatives.     

A new, one-pot, three-component synthesis of 4H-pyrido[1,2-a]pyrimidines, 4H-pyrimido[1,2-a]pyrimidines, and 4H-pyrazino[1,2-a]pyrimidines

A new, one-pot and three-component synthesis of 4H-pyrido[1,2-a]pyrimidines, 4H-pyrimido[1,2-a]pyrimidines, and 4H-pyrazino[1,2-a]pyrimidines is described. The reactive 1:1 zwitterionic intermediate, formed by the addition of isocyanides to dialkyl acetylenedicarboxylates, was trapped by N-(2-heteroaryl)amides to yield a ketenimine intermediate, which was cyclized and then rearranged under the reaction conditions to afford the title compounds under mild reaction conditions in good yields. Single-crystal X-ray analysis conclusively confirms the structure of the obtained bridgehead bicyclic 6-6 heterocyclic compounds.     

Formation of O(3P) atoms and epoxides from the gas- phase reaction of O3 with isoprene

The formation yields of 1,2-epoxy-2-methyl-3-butene and 1,2-epoxy-3-methyl-3-butene have been measured from the reaction of O₃ with isoprene at room temperature and one atmosphere total pressure of N₂ and air diluents, with and without cyclohexane to scavenge the OH radicals formed in this reaction system. In addition, a relative rate method was used to determine a rate constant for the gas-phase reaction of O₃ with 1,2-epoxy-2-methyl-3-butene of (2.5 ± 0.7) x 10^-18 cm³ molecules^-1 s^-1 at 296 ± 2 K. Our data show that the epoxide yields in N₂ and air diluents are the same, with formation yields of 1,2-epoxy-2-methyl-3-butene of 0.028 ± 0.007 and of 1,2-epoxy-3-methyl-3-butene of 0.011 ± 0.004. These data further show that the epoxides arise from the primary O₃ reaction with isoprene, and not via the formation of O(³P) atoms from the O₃ - isoprene reaction followed by reaction of these O(³P) atoms with isoprene.     

The oxidation of hydrazine derivatives with 4-phenyl-1,2,4-triazoline-3,5-dione

The oxidation of benzophenone hydrazone with 4-phenyl-1,2,4-triazoline-3,5-dione (PTD) yields benzophenone azine which is also formed from the reaction of the hydrazone with the ylid obtained from diphenyldiazomethane and PTD; the ylid forms a stable addition product with ethanol. With PTD, carbohydrazides are converted to 1,2-diacylhydrazines and small amounts of the corresponding azides; in contrast, p-toluenesulfonylhydrazine yields p-toluenesulfinic acid, isolated as its adduct with PTD, 1-(p-toluenesulfonyl)-4-phenylurazole. Possible mechanisms to rationalize the formation of these products are discussed.     

Synthesis of conjugated enynes from ketones and aldehydes by 1,2-CC insertion and 1,2-CH insertion of carbenoids as the key reactions

The addition reactions of 1-chlorovinyl p-tolyl sulfoxides, which were derived from ketones and chloromethyl p-tolyl sulfoxide, with lithium acetylides gave adducts in moderate to good yields. Treatment of the adducts with Grignard reagents resulted in the formation of conjugated enynes in good to high yields via the 1,2-carbon-carbon insertion (1,2-CC insertion) reaction of the generated magnesium carbenoid intermediates. On the other hand, the addition reactions of 1-chlorovinyl p-tolyl sulfoxides derived from aldehydes with lithium acetylides directly gave conjugated enynes bearing a p-tolyl sulfinyl group at the 1-position through the 1,2-carbon-hydrogen insertion (1,2-CH insertion) reaction of the generated lithium carbenoid intermediates. These procedures provide a good way for the synthesis of multi-substituted conjugated enynes from ketones and aldehydes.     

Enantioselective Michael addition of aldehydes to maleimides organocatalysed by chiral 1,2-diamines: an experimental and theoretical study

Simple and commercially available chiral 1,2-diamines were used as organocatalysts for the enantioselective conjugate addition of aldehydes, including α,α-disubstituted, to maleimides. The reaction was carried out in the presence of hexanedioic acid as an additive in aqueous solvents at room temperature. By employing (1S,2S)- and (1R,2R)-cyclohexane-1,2-diamine as organocatalysts, the corresponding Michael adducts bearing new stereocenters were obtained in high or quantitative yields with enantioselectivities of up to 92%, whereas the use of (1S,2S)-1,2-diphenylethane-1,2-diamine gave a much lower ee. Theoretical calculations were used to justify the observed sense of the stereoinduction.     

A novel, one-pot, three-component synthesis of 4H-pyrido[1,2-a]pyrimidines

A novel, one-pot, three-component synthesis of 4H-pyrido[1,2-a]pyrimidines is described. The reactive 1:1 zwitterionic intermediate, formed by the addition of isocyanides to dialkyl acetylenedicarboxylates, was trapped by N-(2-pyridyl)amides to produce the title compounds under mild reaction conditions in good yields.     

One-pot three-component reaction of isocyanides, dialkyl acetylenedicarboxylates and phthalhydrazide: synthesis of highly functionalized 1H-pyrazolo[1,2-b]phthalazine-5,10-diones

Protonation of the highly reactive 1:1 intermediate produced in the reaction between alkyl isocyanides and electron-deficient acetylenic esters with phthalhydrazide, leads to a vinylisonitrilium cation, which undergoes an addition reaction with the conjugate base of the phthalhydrazide to produce dialkyl 3-(alkylamino)-5,10-dioxo-5,10-dihydro-1H-pyrazolo[1,2-b]phthalazine-1,2-dicarboxylates in fairly good yields at room temperature.     

Preparation of (E)-1-aryl-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-propenes via stereoselective bissilylation of trifluoromethyl aryl acetylenes and electrophilic substitution of its TMS groups

Preparations and reactions of (E)-1-aryl-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-propenes are described. (E)-1-Aryl-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-propene was prepared from aryl trifluoromethyl acetylenes via reductive bissilylation by TMSCl/Mg in good yields. The silyl groups of (E)-3,3,3-trifluoro-1,2-di(trimethylsilyl)-1-phenyl-1-propene were substituted by electrophiles in both a stepwise and stereoselective (and/or stereospecific) manner. This compound could be a building block for preparations of substituted trifluoropropenes.     

Chiral diphenylselenophosphoramides: a new class of chiral ligands for the titanium(IV) alkoxide-promoted addition of diethylzinc to aldehydes

Chiral C₂-symmetric diphenylselenophosphoramides 1 and 2 were prepared from the reaction of diphenylselenophosphinic chloride with (1R,2R)-(−)-1,2-diaminocyclohexane and (1R,2R)-(+)-1,2-diphenylethylenediamine, respectively, in high yields. Another novel chiral ligand 3 was prepared from the reaction of diphenylselenophosphinic chloride with (R)-(+)-1,1′-binaphthyl-2,2′-diamine using butyllithium as the base. The ligands were used as catalytic chiral ligands in the titanium(IV) alkoxide-promoted enantioselective addition reaction of diethylzinc to aldehydes.     

Electrospray mass analysis of chemical oxidation of 1,2-diarylcyclopropanes by Cu(II) salt

Electrospray ionization mass spectrometry was used to study chemical electron-transfer reactions of 1,2-diarylcyclopropanes by Cu(II) salt in acetonitrile. The ion [M ? H]⁺ with a hydrogen atom loss and the solvent adduct ions, [M+42]⁺, etc., were detected as the initial reaction products, where [M+42]⁺ represents the ion whose mass is 42 u greater than the parent molecule M. From the study of deuterated derivatives, the hydrogen abstraction was revealed to occur at the 3 position of the cyclopropanes, and the mechanism of the hydrogen abstraction reaction and of the solvent addition were discussed.     

Facile monoprotection of trans-1,2-diaminocyclohexane

A new method of monoprotection of C₂-symmetric trans-1,2-diaminocyclohexane as the N-phthaloyl, N-tetrachlorophthaloyl or N-1,8-naphthaloyl derivative is presented. The first two derivatives are obtained with high yields and can be readily transformed into other unsymmetrical derivatives of trans-1,2-diaminocyclohexane.     

Stereocontrolled approach to 1-azabicyclo[4.1.0]heptanes: application to the synthesis of trans-2,6-disubstituted piperidines

Stereocontrolled synthesis of a 1-azabicyclo[4.1.0]heptane is achieved by formation of an NH aziridine from the corresponding 1,2-azido alcohol and subsequent intramolecular conjugate addition onto a tethered α,β-unsaturated ester. Regioselective ring opening of the product at C-7 by heteroatom based nucleophiles yields trans-2,6-disubstituted piperidines in moderate to good yields.     

Facile synthesis of 1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives by a one-pot, three-component reactions

Protonation of the highly reactive 1:1 intermediate produced in the reaction between alkyl or aryl isocyanides and electron-deficient acetylenic esters with 3,6-dihydroxypyridazine, leads to a vinylisonitrilium cation, which undergoes an addition reaction with the conjugate base of the 3,6-dihydroxypyridazine to produce dialkyl 3-(alkyl or arylamino)-5,8-dioxo-5,8-dihydro-1H-pyrazolo[1,2-a]pyridazine-1,2-dicarboxylates in good yields at room temperature.