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Mechanistic Study of the Rhodium‐Catalyzed [3+2+2] Carbocyclization of Alkenylidenecyclopropanes with Alkynes
Author(s) -
Yu Haizhu,
Lu Qianqian,
Dang Zhimin,
Fu Yao
Publication year - 2013
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201300575
Subject(s) - alkyne , alkene , regioselectivity , chemistry , steric effects , cyclopropane , catalytic cycle , reductive elimination , rhodium , oxidative addition , medicinal chemistry , stereochemistry , catalysis , organic chemistry , ring (chemistry)
A systematic theoretical study has been performed on the recently reported Rh I ‐catalyzed [3+2+2] carbocyclization reactions between alkenylidenecyclopropanes (ACPs) and alkynes. With the aid of theoretical calculations, two possible mechanisms, that is, alkene‐carbometalation‐first and alkyne‐carbometalation‐first mechanisms, are examined in this study. In the oxidative addition step, the possibility of reaction on either the distal or proximal CC bond of the cyclopropane group has been evaluated. The calculations indicate that the alkene‐activation‐first mechanism is more favored for the overall catalytic cycle. This mechanism involves four steps, that is, oxidative addition of the distal (rather than the proximal) CC bond of cyclopropane group, alkene carbometalation , alkyne carbometalation , and reductive elimination. The rate‐determining step in the overall catalytic cycle is the carbometalation of the alkyne (i.e., the alkyne‐insertion step) and this step also determines the regioselectivity. Finally, the origin of the regioselectivity is determined by the steric effect (i.e., the steric crowding between the electron‐withdrawing group on alkyne and other ligands on the rhodium center) in the alkyne‐insertion step.