Catalytic Asymmetric Syntheses of Alkylidenecyclopropanes from Allenoates with Donor‐Acceptor and Diacceptor Diazo Reagents

Abstract

The first diastereo-and enantioselective cyclopropanation reactions of electron-deficient allenes with donor-acceptor and diacceptor diazo reagents are described. The desired enantioenriched alkylidenecyclopropanes (ACPs) were obtained in high yields with high diastereo-and enantioselectivities in the presence of Rh 2 ((S)-TCPTAD) 4 or Rh 2 ((R)-BTPCP) 4 catalysts (up to 95 % yield, > 95 : 5 d.r. and 99 : 1 e.r.). This methodology gave a direct access to ACPs bearing multiple electron-deficient substituents and allows to further expand the availability of ACPs chemistry. Interestingly, during the examination of the scope of this reaction, the asymmetric intramolecular CÀ H insertion reaction into tert-butyl group was observed as a side reaction with up to 94 : 6 e.r.

Enantio- and Diastereodivergent Cyclopropanation of Allenes by Directed Evolution of an Iridium-Containing Cytochrome

“…Finally, the two faces of the terminal alkene of a 1,1-disubstituted, unsymmetrical allene are diastereotopic and lead to ( E )- and ( Z )-configurations of the products. Thus, only five examples of undirected, enantioselective cyclopropanation of achiral allenes with ee >90% have been reported, − despite a rich history of stereochemical studies of ACPs, and these five examples circumvent the aforementioned challenges by using a carbene that is sterically bulky , or that contains a second binding site for the metal and an excess of allene . Because few allenes are commercially available, selective cyclopropanation with a limiting allene is the appropriate stoichiometry for synthetic applications.…”