34780-69-3Relevant academic research and scientific papers
Synthesis of novel-dl-α-tocopherol-based and sterically-hindered-phenol-based monomers and their utilization in copolymerizations over metallocene/MAO catalyst systems. A strategy to remove concerns about additive compatibility and migration
Auer, Markku,Nicolas, Ronan,Rosling, Ari,Wilen, Carl-Eric
, p. 8346 - 8352 (2007/10/03)
In this paper we present an initial study on various synthetic routes to novel polymerizable dl-α-tocopherol derivatives and to a styrenic sterically hindered phenol which was stimulated by our desire to conduct copolymerization with these monomers with α-olefins over different metallocene/ methylalumoxane (MAO) catalyst systems. The syntheses of 6-hydroxyl-2,5,7,8-tetramethyl-2-(but-3-enyl)-chroman (1) and 5,7,8-trimethyl-3-(hex-5-enyl)benzofuran-6-ol (2-) were achieved by cyclocondensation of trimethylhydroquinone (TMHQ) with 3-methylhept-1,6-dien-3-ol and 2,7-octadienol, respectively. However, the latter tocopherol compound (2) could only be obtained in low yields, and all our attempts to isolate the product from its ring-opened isomers failed. This can be attributed to the fact that the reaction between TMHQ and 2,7-octadienol gave rise to a highly complex reaction mixture. Compound 3, 6-hydroxyl-2,2,8,9-tetramethyl-6-allylchroman, was prepared from the corresponding allylchromanoxy ether via Claisen rearrangement. In addition facile synthetic pathways to 4-methylene(3,5-di-tert-butyl-4-phenoxy)styrene (4) and its trimethylsilylated derivative 5, i.e., 4-methylene(3,5-di-tert-butyl-4-trimethylsiloxyphenyl)-styrene, were successfully developed. The chromanol 1 was copolymerized with ethylene over a rac-[dimethylsilylenebis(4,5,6,7-tetrahydro-1-indenyl)]zirconium dichloride/MAO catalyst system, and monomers 4 and 5 were copolymerized with styrene over an (η5-indenyl)trichlorotitanium (IndTiCl3)/MAO catalyst system. The copolymers contained from 2.3 to 6.8 wt % functional units and exhibit enhanced thermooxidative stabilities in comparison to the corresponding homopolymers as determined by TGA and DSC analysis.
Intramolecular radical-chain hydrosilylation catalysed by thiols: Cyclisation of alkenyloxysilanes
Cai, Yudong,Roberts, Brian P.
, p. 467 - 475 (2007/10/03)
Alkenyloxy(diphenyl)silanes that contain a terminal double bond undergo radical-chain cyclisation at 60-65°C, in the presence of di-tert-butyl hyponitrite as initiator and a thiol as a catalyst. The thiol acts as a polarity-reversal catalyst and promotes the overall abstraction of hydrogen from the Si-H group in the alkenyloxysilane by the cyclic carbon-centred radical, formed by intramolecular addition of the corresponding silyl radical to the C=CH2 group. Allyloxysilanes give five-membered-ring products via 5-endo-trig cyclisation of the intermediate allyloxysilyl radical. Homoallyloxysilanes give mixtures of five- and six-membered heterocycles, but the intermediate silyl radicals undergo predominantly 6-endo cyclisation, in contrast to the corresponding carbon-centred radicals which cyclise preferentially in the 5-exo mode. An analogous pentenyloxysilane gives only the seven-membered-ring product via a 7-endo radical cyclisation. Steric effects play an important part in influencing the final-product stereochemistry when this is determined in the hydrogen-atom transfer reaction between the cyclic adduct radical and the thiol catalyst. Complementary EPR spectroscopic studies of the short-lived intermediate cyclic adduct radicals have been carried out in the absence of thiol and the structures and conformations of these species have been determined. It is emphasised that, for thiol catalysis of the overall cyclisation of alkenyloxysilanes to be successful, it is necessary for the addition of the chain-carrying thiyl radical to the C=CH2 group to be reversible under the reaction conditions.
COPPER (I) CATALYSIS OF OLEFIN PHOTOREACTIONS -9. PHOTOBICYCLIZATION OF alpha -, beta -, AND gamma -ALKENYLALLYL ALCOHOLS.
Salomon,Coughlin,Ghosh,Zagorski
, p. 998 - 1007 (2007/10/14)
Cyclobutylcarbinyl alcohols of the bicyclo left bracket 3. 2. 0 right bracket heptane ring system are produced by UV irradiation of alpha -, beta -, and gamma -alkenylallyl alcohols in the presence of copper (I) trifluoromethanesulfonate (CuOTf). endo-2-Hydroxy epimers of bicyclo left bracket 3. 2. 0 right bracket heptan-2-ols are generated stereoselectively. This result as well as the effect of CuOTf on the **1H NMR spectrum of 4,4-dimethyl-1,6-heptadien-3-ol suggests that coordination of two C equals C bonds and the hydroxyl group with a single copper (I) is important. The derived bicyclo left bracket 3. 2. 0 right bracket heptan 2-ones fragment cleanly at 580 degree C to afford cyclopent-2-en-1-ones. Geometric isomerization competes with photobicyclization of (E)- and (Z)-octa-2,7-dien-1-ols.
