et al
To account for the distinct regioselectivity,
Ravikumar group postulated
possible reaction mechanisms that are summarized in Scheme 2.
[Cp*RhCl2]2 firstly reacts with
Ag2CO3 to generate active catalyst
Cp*RhCO3 (cat ), which is followed by
the ligand exchange with
cyclopropanol R’ to afford alkoxide compound I . FromI , there exist two possible pathways (path a or path b). In
path a, β -carbon elimination would take place to afford
alkyl-rhodium homoenolate II . Then, with the participant of
another molecule of cyclopropanol, the successive ligand exchange andβ -carbon elimination occur to give dialkyl-rhodium speciesIV . In contrast, the ligand exchange with the second molecule
of cyclopropanol prior to β -carbon elimination would yield
species IV through compound II’ (path b). Finally,
reductive elimination from speciesIV leads to 1,6-diketone P . It should be noted that
the β -hydride eliminated product P’ could not be
obtained in this reaction. As shown in Scheme 2, in the absence of
[Cp*RhCl2]2, cyclopropanol would
undergo the ring-opening to give monoketone product catalyzed by
Ag2CO3.
SCHEME 2 Possible reaction mechanisms
proposed by
Ravikumar’s group
Although the plausible mechanistic pathway has been proposed by the
Ravikumar group, some key issues still need to be addressed: (1) In this
experiment, the role of the
catalyst [Cp*RhCl2]2 and additive
Ag2CO3 is still unclear; (2) It is
unclear which steps determine the selectivity and what are the origins
of that observation in this experiment; (3) The β -hydride
eliminated product was not obtained in reaction A – it would be
interesting to investigate the corresponding factors. To address these
questions, a theoretical investigation of the detailed reaction
mechanisms is needed. Herein, we report our detailed density functional
theory (DFT) calculations on the reaction mechanisms, in order to gain
insight into the interesting experimental observations and distinct
selectivity. We expect that this work will help to understand the
detailed reaction mechanisms and to design new related reactions.