Highly enantioenriched homoenolate reagents by asymmetric gamma-deprotonation of achiral 1-silyl-substituted 1-alkenyl carbamates |
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Authors: | Reuber Jenny Fröhlich Roland Hoppe Dieter |
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Institution: | Organisch-Chemisches Institut, Westf?lische Wilhelms-Universit?t Münster, Corrensstrasse 40, 48149 Münster, Germany. |
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Abstract: | 1-trimethylsilyl-1-alkenyl carbamates 1 are deprotonated by n-butyllithium/(-)-sparteine (2) with a high degree of enantiotopic differentiation in the gamma-position to form the enantiomerically enriched allyllithium derivatives 3. Trapping these with several electrophiles proceeds stereospecifically in an anti-S(E)' or syn-S(E)' substitution to form products 4 or ent-4, respectively. Compounds 3a (R = Me) and 3b (R = Ph) exhibit toward carbonyl electrophiles opposite senses of almost complete stereospecificity, thus for 3b.2 the involvement of a eta(3)-complex is suggested. reaction: see text] |
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