20° SEMINARIO QUÍMICA ORGÁNICA IQUIR 2020

SEMINARIO QUÍMICA ORGÁNICA 05-10-20

EXPOSITOR: Qco. Juan Ramos

TÍTULO: "Cicloadición [2+2] de alenos"

FUENTE: Johannes. M. Wiest, Michael L. Conner, and M. Kevin Brown, Allenoates in Enantioselective [2+2] Cycloadditions: From a Mechanistic Curiosity to a Stereospecific Transformation, J. Am. Chem. Soc. 2018, 140, 15943−15949.

DÍA, HORA y LUGAR: Lunes 5 de octubre de 2020, 18:00 h, Plataforma MEET GOOGLE.

Link: meet.google.com/bfh-poxv-bso

RESUMEN: Identification of a novel catalyst−allenoate pair allows enantioselective [2+2] cycloaddition of α-methylstyrene. To understand the origin of selectivity, a detailed mechanistic investigation was conducted. Herein, two competing reaction pathways are proposed, which operate simultaneously and funnel the alkenes to the same axially chiral cyclobutanes. In agreement with the Woodward− Hoffmann rules, this mechanistic curiosity can be rationalized through a unique symmetry operation that was elucidated by deuteration experiments. In the case of 1,1-diarylalkenes, distal communication between the catalyst and alkene is achieved through subtle alteration of electronic properties and conformation. In this context, a Hammett study lends further credibility to a concerted mechanism. Thus, extended scope exploration, including β-substitution on the alkene to generate two adjacent stereocenters within the cyclobutane ring, is achieved in a highly stereospecific and enantioselective fashion (33 examples, up to >99:1 er).