期刊
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
卷 2005, 期 24, 页码 5236-5241出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.200500553
关键词
aryl-aryl coupling; arynes; buttressing effects; nucleophilic addition; regioselectivity; trialkylsilyl groups
(2,6-Dichlorophenyl)trimethyl- and -triethylsilane exhibit untypical reactivity patterns toward strong bases. When treated at -100 degrees 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 degrees C to set free didehydrobenzenes (arynes) which are trapped by their aryllithium. precursors. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
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