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■ Theoretical Investigation of Cp*Co(III)-Mediated Regioselective [4 + 2]-Annulation of N-Chlorobenzamide with Vinyl Acetate for the Synthesis of Isoquinolone

Nan Lu,* Chengxia Miao, and Xiaozheng Lan

*College of Chemistry and Material Science, Shandong Agricultural University, No.61 Daizong Street, Taian 271018, China

Abstract

The mechanism is investigated for regioselective [4 + 2]-annulation of N-chlorobenzamide catalyzed by Cp*Co(III). The CoCp*(OAc)2-mediated ortho-cobaltation via acetate-aided N-H and C−H deprotonation furnishes a five-membered intermediate, which is coordinative inserted into alkene by giving seven-membered cobaltacycle. The reductive elimination and oxidative addition of CoCp*(I) species afford six-membered ring. The recovery of CoCp*(III) is assisted by one AcOH for vinyl acetate with OAc group available to cleavage as one ligand. Two OAc ligands are both supplied by AcOH for vinyl ketone with COMe group difficult to break. The acetate-assisted tautomerization produces isoquinolin-1(2H)-one. The 3-acetylisoquinolin-1(2H)-one is given by dehydrooxidation. The promotion of Cp*Co(III) lies in the barrier decrease of most steps especially N-H and C−H deprotonation. AcOH functions in the protonation of Cl, N and as sources of acetate ligands for the recovery of CoCp*(III). These results are supported by Multiwfn analysis on FMO of specific TSs and MBO value of vital bonding, breaking.