651027-06-4Relevant academic research and scientific papers
Fluorine-flanked congested sites: Minimal, though perceptible buttressing effects on the proton mobility of arenes
Heiss, Christophe,Leroux, Frederic,Schlosser, Manfred
, p. 5242 - 5247 (2007/10/03)
(2,6-Difluorophenyl)trimethylsilane, -triethylsilane and -triisopropylsilane undergo sec-butyllithium-mediated metalation at the 3- and 4-position (ortho and meta relative to the halogen) in ratios of 99.6:0.4, 98:2 and 95:5, respectively. The steric pressure transmitted by the fluorine atoms can be increased if the trialkylsilyl group is locked up on the other side by a relatively voluminous substituent. Whereas (2,6-difluorophenyl)triethylsilane is attacked by lithium 2,2,6,6-tetramethylpiperidide under deprotonation of the 4- and 5-position in a ratio of 99.4:0.6, the proportion of "ortho"/ "meta" metalation changes to 84:16 when (2-bromo-6-fluorophenyl) triethylsilane acts as the substrate. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
Exploring Structural Opportunities: The Regioflexible Substitution of 1,3-Difluorobenzene
Schlosser, Manfred,Heiss, Christophe
, p. 4618 - 4624 (2007/10/03)
To demonstrate the superiority of modern organometallic methods, the inexpensive starting material 1,3-difluorobenzene has been selectively converted into the three benzoic acids and all seven bromobenzoic acids containing the two fluorine atoms in homovicinal positions. The 2,6-difluorobenzoic acid (1) was prepared in a one-pot reaction consisting of direct metallation and carboxylation. The key step on the route to the bromobenzoic acid 4 was a deprotonation-triggered bromine migration from the 2- to the 4-position. All other products were attained through (2,6-difluorophenyl)triethylsilane (11). Consecutive deprotonation of the sites adjacent to the fluorine atoms, followed by appropriate electrophilic substitution, provided not only the acid 7 but also the dibromo and iodobromo derivatives 13 and 23. These in turn gave the isomers 14 and 24 upon base-mediated migration of the heaviest halogen, which made the acids 8 and 10 directly accessible. The regiocontrolled monodebromination of intermediate 14 afforded (4-bromo-2,6-difluoro)triethylsilane (15), which opened the route to the acids 3 and 5 (by carboxylation and protodesilylation) and to acid 9 (by carboxylation and bromodesilylation). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
