Theoretical Mechanistic Studies on Methyltrioxorhenium-Catalyzed Olefin Cyclopropanation: Stepwise Transfer of a Terminal Methylene Group

Methyltrioxorhenium
(MTO)-catalyzed transfer of a methylene group
to styrene has been computationally found to preferably follow a stepwise
mechanism to give phenylcyclopropane via formation of a pseudo-metallacyclic
intermediate and subsequent alkylative cyclization. The present result
serves as the first theoretical evidence for d0 transition
metal mediated transfer of methylene as a terminal form rather than
a metal carbene or carbenoid fashion, accompanied by the cleavage
of a H2CO double bond. The mechanism presented
here is in contrast to the carbenoid or metal carbene promoted methylene
transfer and to the MTO-catalyzed isoelectronic atom (group) transfer
in MeRe­(O)2(η2-O–NH) or MeRe­(O)2(η2-O–O). This study not only enriches
the chemistry of olefin cyclopropanation and the MTO-catalyzed group
(atom) transfer event but also sheds new light on the reaction chemistry
of formaldehyde.