ol0364677_si_002.cif (16 kB)

Highly Enantioenriched Homoenolate Reagents by Asymmetric γ-Deprotonation of Achiral 1-Silyl-Substituted 1-Alkenyl Carbamates

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posted on 04.03.2004, 00:00 by Jenny Reuber, Roland Fröhlich, Dieter Hoppe
1-Trimethylsilyl-1-alkenyl carbamates 1 are deprotonated by n-butyllithium/(−)-sparteine (2) with a high degree of enantiotopic differentiation in the γ-position to form the enantiomerically enriched allyllithium derivatives 3. Trapping these with several electrophiles proceeds stereospecifically in an anti-SE‘ or syn-SE‘ 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 η3-complex is suggested.