Thermal decomposition of poly(sec-amyl methacrylate)

The thermal decomposition of poly(sec-amyl methacrylate) is studied by simultaneous thermogravimetry–gas chromatography–mass spectrometry and by pyrolysis–gas chromatography. The TG curve has four distinct breaks and a plateau. Results of the identification of the evolved gas at the individual breaks by GC–MS techniques lead to the conclusion that these breaks correspond to the individual processes in the decomposition mechanism like that of poly(tert-butyl methacrylate): the first break, the depolymerization initiated at the unsaturated chain ends; the second break, the depolymerization initiated at the saturated chain ends; the third break, the ester decomposition; the plateau, the inhibition of decomposition by the formation of poly(methacrylic anhydride); the fourth break, the decomposition of poly(methacrylic anhydride). The extent of ester decomposition is related to the substituent constants based on Hammett equation. The ester decomposition product is separated into three pentene isomers by pyrolysis–gas chromatography: trans-2-pentene, cis-2-pentene, and 1-pentene. As raising decomposition temperature, the composition ratio of trans-2-pentene decreases and becomes constant above 620 K, and the composition ratios of cis-2-pentene and 1-pentene increase and also become constant above 620 K. These results are accounted for by mobility of atoms included in the substituent at forming a ring transition state.     

Reaction of alkynyltrimethylsilanes with a hypervalent organoiodine compound: A new general synthesis of alkynyliodonium salts

New general methods for the synthesis of alkynyl(phenyl)iodonium tetrafluoroborate 2 from alkynyltrimethylsilanes 1 utilizing the combination of iodosylbenzene and triethyloxonium tetrafluoroborate or boron trifluoride etherate were developed. The medium effect observed in the reaction was also discussed.     

Site-specific alkylation of tetra-alkylpyrroles

Intramolecular cyclisation of the trifluoromethanesulphonate esters of the β-(4-hydroxy-n-butyl)-pyrroles (5a) and (5b) in each case yields a mixture of the α- and β-alkylated products whereas exclusive β-alkylation is observed for the β-(5-hydroxy-n-pentyl)-pyrrole (5c).     

Synthesis and characterization of beta-haloalkenyl-lambda3-bromanes: stereoselective Markovnikov addition of difluoro(aryl)-lambda3-bromane to terminal acetylenes

Reported here for the first time are the synthesis, isolation, and characterization of hypervalent beta-haloalkenyl-lambda3-bromanes. Exposure of terminal alkynes to p-trifluoromethylphenyl(difluoro)-lambda3-bromane activated by BF3-i-Pr2O resulted in fluoro-lambda3-bromanation of the triple bonds in a Markovnikov fashion, yielding (E)-beta-fluoroalkenyl-lambda3-bromanes stereoselectively in good yields. 5-Chloro-1-pentynes undergo domino lambda3-bromanation-chlorine shift-fluorination or lambda3-bromanation-chlorine shift-alkyl shift-fluorination reaction, depending on the substituents and afford (E)-beta-chloroalkenyl-lambda3-bromanes stereoselectively in high yields. The beta-chloroalkenyl-lambda3-bromanes contain three kinds of halogen atoms, F, Cl, and Br, in the molecule.     

Iodobenzene-catalyzed alpha-acetoxylation of ketones. in situ generation of hypervalent (diacyloxyiodo)benzenes using m-chloroperbenzoic acid

Reported here for the first time is the iodobenzene-catalyzed alpha-oxidation of ketones, in which diacyloxy(phenyl)-lambda3-iodanes generated in situ act as real oxidants of ketones and m-chloroperbenzoic acid serves as a terminal oxidant. Oxidation of a ketone with m-chloroperbenzoic acid in acetic acid in the presence of a catalytic amount of iodobenzene, BF3.Et2O, and water at room temperature under argon affords an alpha-acetoxy ketone in good yield. p-Methyl- and p-chloroiodobenzene also serve as efficient catalysts in this direct oxidation. We found that when the reaction was carried out in the absence of a catalytic amount of iodobenzene, Baeyer-Villiger oxidation of a ketone took place. It is noted that use of water and BF3.Et2O is crucial to the success of this alpha-acetoxylation.     

Domino Michael addition-carbene rearrangement-cyclization reaction of 1-alkynyl(aryl)-lambda3-bromanes with 2-mercapto-1,3-benzazoles

Exposure of 1-alkynyl[p-(trifluoromethyl)phenyl](tetrafluoroborato)-lambda3-bromanes to 2-mercaptobenzimidazole or benzothiazole in dichloromethane at 0 degrees C under argon resulted in a domino Michael addition-carbene rearrangement-cyclization reaction to produce directly tricyclic heterocycles in high yields, whereas the reaction with 2-mercaptobenzoxazole afforded 1-alkynyl sulfides.     

Addition to electron deficient olefins of alpha-oxy carbon- centered radicals, generated from cyclic ethers and acetals by the reaction with alkylperoxy- lambda(3)-iodane

Thermal decomposition of 1-tert-butylperoxy-1,2-benziodoxol-3(1H)-one in cyclic ethers and acetals at 50 degrees C generates alpha-oxy carbon-centered radicals, which undergo an addition reaction with vinyl sulfones and unsaturated esters.     

Syntheses of a series of octaethylporphyrin-benzoquinone linked molecules as a model for the primary process of photosynthesis

To clarify the primary process of photosynthesis, a series of model compounds, in which an octaethylporphyrin and a benzoquinone ring are connected with different lengths of a polymethylene chain, were synthesized and their photophysical properties were investigated.