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000009772 0247_ $$2DOI$$a10.1002/ejoc.201000410
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000009772 084__ $$2WoS$$aChemistry, Organic
000009772 1001_ $$0P:(DE-HGF)0$$aScholz, R.$$b0
000009772 245__ $$aEnantioselective Synthesis, Configurational Stability, and Reactivity of Lithium a-tert-Butylsulfonyl Carbanion Salts
000009772 260__ $$aWeinheim$$bWiley-VCH Verl.$$c2010
000009772 300__ $$a4588 - 4616
000009772 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article
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000009772 440_0 $$01958$$aEuropean Journal of Organic Chemistry$$v2010$$x1434-193X$$y24
000009772 500__ $$aThis research was supported by the Deutsche Forschungsgemeinschaft (DEG), Volkswagen Foundation, and Fonds der Chemischen Industrie. We thank D. Wolters for his help with the graphics.
000009772 520__ $$aThe reactions of enantiopure S-tert-butyl sulfones of the type (RCH)-C-I(R-2)SO(2)tBu (<= 99 % ee) with lithiumorganyl compounds gave the corresponding chiral alpha-sulfonyl carbanion salts [(RC)-C-1(R-2)SO(2)tBu]Li with >= 94 % ee. The enantioselectivity of the deprotonation of the phenyl-but not dialkyl-substituted sulfones is strongly dependent on the nature of the lithiumorganyl. Because of this observation and the strong decrease in enantioselectivity in the presence of TMEDA and HMPA, we propose an intramolecular proton transfer following complexation of the sulfone by RLi. Racemization of (RC)-C-1(R(2))SO(2)tBu]Li follows first-order kinetics and seems to be mainly an enthalpic process with a small negative activation entropy, as revealed by polarimetric measurements at low temperatures. This is in accordance with C-alpha-S bond rotation as the rate-determining step. The salts [(RC)-C-1(R-2)SO(2)tBu]Li have half-lives of racemization in the order of several hours at -105 degrees C. The deuteriation of the salts at -105 degrees C with CF3CO2D proceeded with enantioselectivities of >= 94 % ee, the magnitude of which was not significantly affected by the presence of TMEDA and HMPA. The salts also reacted with carbon-based electrophiles at low temperatures with high enantioselectivity. The conversion of (RCH)-C-1(R-2)SO(2)tBu via [(RC)-C-1(R-2)SO(2)tBu]Li to (RC)-C-1(R-2,E)SO(2)tBu, which involves the loss of stereogenicity at the alpha-stereogenic center and its reestablishment upon reaction of the chiral carbanian with electrophiles, occurred with high overall enantioselectivity. Electrophiles attack the anionic C atom of [(RC)-C-1(R-2)SO(2)tBu]Li with high selectivity on the side syn to the O atoms and anti to the tert-butyl group. The reactivity of the dialkyl-substituted salts [(RC)-C-1(R-2)SO(2)tBuiLi (R-1, R-2 = alkyl) is significantly higher than that of the benzylic salts [RC(Ph)SO(2)tBu]Li (R = alkyl) and the HMPA-coordinated SIPs of [MeC(Ph)SO(2)tBu]Li are significantly more reactive towards EtI than the corresponding O-Li contact ion pairs.
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000009772 650_7 $$2WoSType$$aJ
000009772 65320 $$2Author$$aChirality
000009772 65320 $$2Author$$aCarbanions
000009772 65320 $$2Author$$aRacemization
000009772 65320 $$2Author$$aEnantioselectivity
000009772 65320 $$2Author$$aAlkylation
000009772 7001_ $$0P:(DE-HGF)0$$aHellmann, G.$$b1
000009772 7001_ $$0P:(DE-Juel1)129146$$aRohs, S.$$b2$$uFZJ
000009772 7001_ $$0P:(DE-HGF)0$$aÖzdemir, D.$$b3
000009772 7001_ $$0P:(DE-HGF)0$$aRaabe, G.$$b4
000009772 7001_ $$0P:(DE-HGF)0$$aVermeeren, C.$$b5
000009772 7001_ $$0P:(DE-HGF)0$$aGais, H.-J.$$b6
000009772 773__ $$0PERI:(DE-600)1475010-7$$a10.1002/ejoc.201000410$$gVol. 2010, p. 4588 - 4616$$p4588 - 4616$$q2010<4588 - 4616$$tEuropean journal of organic chemistry$$v2010$$x1434-193X$$y2010
000009772 8567_ $$uhttp://dx.doi.org/10.1002/ejoc.201000410
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