- Combined Directed ortho Metalation/Suzuki-Miyaura cross-coupling strategies. Regiospecific synthesis of chlorodihydroxybiphenyls and polychlorinated biphenyls
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(Chemical Equation Presented) The Directed ortho Metalation (DoM)/Suzuki-Miyaura cross-coupling strategy is applied for the regiospecific construction of all isomeric monochloro and selected dichloro and trichloro 2,3-dihydroxybiphenyls (DHBs). The combined methodology highlights iterative DoM processes, hindered Suzuki-Miyaura couplings, and advantages in diversity in approaches from commercial starting materials leading to provision of chloro-DHBs as single isomers in high purity and on a gram scale. The syntheis of several PCBs are also reported.
- Nerdinger,Kendall,Cai,Marchart,Riebel,Johnson,Yin,Henaff,Eltis,Snieckus
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p. 5960 - 5967
(2008/02/09)
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- meta- rather than ortho-directed metalations: Buttressing effects prejudicing the proton abstraction from (2,6-dihalophenyl)silanes
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(2,6-Dichlorophenyl)trimethyl- and -triethylsilane exhibit untypical reactivity patterns toward strong bases. When treated at -100°C with lithium 2,2,6,6-tetramethylpiperidide, they give rise to two, with sec- or tert-butyllithium even three, different organometallic intermediates which can be intercepted with standard electrophiles. The trialkylsilyl group intervenes in two respects. Exerting steric pressure on the neighboring chlorine atoms, it facilitates the permutational displacement of one of them against lithium, a side reaction which occurs whenever alkyllithium compounds are employed. At the same time it impedes the attack of hydrogen atoms by the base in the immediate vicinity of the halogens due to relay transmission of steric hindrance. As a consequence, deprotonation occurs preferentially or exclusively at the 5-("meta") rather than the 4-("ortho")position. 4-Lithiated species, generated as by-products or separately by permutational halogen/metal interconversion, eliminate lithium chloride at -75°C to set free didehydrobenzenes ("arynes") which are trapped by their aryllithium precursors. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
- Heiss, Christophe,Cottet, Fabrice,Schlosser, Manfred
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p. 5236 - 5241
(2007/10/03)
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- Synthesis of polychlorinated biphenyls (PCBs) using the Suzuki-coupling
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An improved synthesis of polychlorinated biphenyls (PCBs) utilizing a palladium-catalyzed cross-coupling reaction (Suzuki-coupling) is described. The coupling of (chlorinated) aryl boronic acids 1-3 with bromochlorobenzenes 4 using the standard conditions of the Suzuki-coupling gave the desired PCB congeners 5-7 in good to excellent yields. The self-coupling product of the aryl boronic acids is the major impurity of this reaction. 3,4,5-trichlorophenyl derivatives such as 10 can be synthesized by coupling of an aryl boronic acid with the corresponding bromochloroaniline 8. The approach offers the advantage of high selectivity and good yields compared to conventional methods Such as the Cadogan reaction and allows the use of less toxic starting materials.
- Lehmler, Hans-Joachim,Robertson, Larry W
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p. 137 - 143
(2007/10/03)
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- Physical, spectral and chromatographic properties of all 209 individual PCB congeners
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Through the use of two capillary GC columns: 40% octadecyl/ 15% phenyl methyl siloxane and 50% phenyl methyl siloxane, it was possible to separate 201 PCB congeners with only four unresolved pairs. The data compiled in this study for all 209 congeners will aid in the identification of selected individual components of these environmental pollutants. The use of this data also presents the opportunity for the improved quantification of the commercial PCB formulations. -from Authors
- Bolgar,et al.
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p. 2687 - 2705
(2007/10/03)
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