Synthesis 2021; 53(22): 4279-4289
DOI: 10.1055/a-1645-2632
special topic
Special Issue dedicated to Prof. Sarah Reisman, recipient of the 2019 Dr. Margaret Faul Women in Chemistry Award

The Trajectory of the (η 5-Cyclopentadienyl)cobalt-Mediated Cycloisomerization of Ene-Yne-Ene-Type Allyl Propargylic Ethers to Furans: A DFT Appraisal

Jonathan J. Wong
a   Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, USA
,
Xiangyang Chen
a   Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, USA
,
a   Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, USA
,
b   Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-1460, USA
› Author Affiliations
This work benefited from pecuniary support by the University of California at Berkeley (K.P.C.V.). We are grateful to the National Science Foundation (CHF-1764328 to K.N.H.) for financial support. Calculations were performed on the Hoffman2 cluster at the University of California, Los Angeles, and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the National Science Foundation (OCI-1053575).


Congratulations to Professor Sarah Reisman at the California Institute of Technology for having been chosen as the first recipient of the Dr. Margaret Faul Award for Women in Chemistry

Abstract

The mechanisms by which the complexes CpCoL2 (Cp = C5H5; L = CO or CH2=CH2) mediate the cycloisomerizations of α,δ,ω-enynenes containing allylic ether linkages are probed by DFT methods. The outcomes corroborate experimental results and provide energetic and structural details of the trajectories leading to 3-(oxacyclopentyl or cycloalkyl)furans via the intermediacy of isolable CpCo-η 4-dienes. They comprise initial stereoselective complexation of one of the double bonds and the triple bond, rate-determining oxidative coupling to a triplet 16e cobalta-2-cyclopentene, and terminal double bond docking, followed by stereocontrolled insertion to assemble intermediate cis- and trans-fused triplet cobalta-4-cycloheptenes. A common indicator of the energetic facility of the latter is the extent of parallel alignment of the alkene moiety and its target Co–Cα bond. The cobalta-4-cycloheptenes transform further by β-hydride elimination–reductive elimination to furnish CpCo-η 4-dienes, which are sufficiently kinetically protected to allow for their experimental observation. The cascade continues through cobalt-mediated hydride shifts and dissociation of the aromatic furan ring. The findings in silico with respect to the stereo-, regio-, and chemoselectivity are in consonance with those obtained in vitro.

Supporting Information



Publication History

Received: 10 August 2021

Accepted after revision: 15 September 2021

Accepted Manuscript online:
15 September 2021

Article published online:
27 September 2021

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