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).
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