Stereospecific Synthesis of Alkenes by Eliminative Cross-Coupling of Enantioenriched sp super(3)-Hybridized Carbenoids

1-Aryl-1,2-dialkylethenes were generated by a sequence of electrophilic substitution, 1,2-metalate rearrangement, and beta -elimination initiated by the addition of enantioenriched alpha -(carbamoyloxy)alkylboronates to enantioenriched lithiated carbamates. The carbenoid stereochemical pairing [i.e., "like"=(S)+(S) or "unlike"=(S)+(R)] and the elimination mechanism (syn or anti), not substituent effects, determined the configuration of the trisubstituted alkene target. For example, (Z)-2,5-diphenyl-2-pentene was produced in 70% yield with E/Z=5:95 by a like combination of Li and Bcarbenoids and syn (thermal) elimination whereas the Eisomer was obtained in the same yield with E/Z>98:2 by an otherwise identical process involving an unlike stereochemical pairing. The concept elaborated overcomes an intrinsic limitation of traditional strategies for direct connective alkene synthesis, which cannot realize meaningful stereochemical bias unless the alkene substituents are strongly differentiated.Original Abstract: Die stereochemische Information, die in einem Paar scalemischer Carbenoid-Reagentien gespeichert ist, bestimmt die Geometrie der Alkene, die durch eliminierende Kreuzkupplung erhalten werden. Die Konfiguration des Alkens wird durch die stereochemische Paarung der Carbenoide (like oder unlike) und den Eliminierungsmechanismus (syn oder anti), aber nicht durch die Substituenten bestimmt.