The Rh/Au-catalyzed regioselective C-8/C-4 alkynylation of N-methylisoquinolone has been theoretically investigated with the aid of density functional theory (DFT) calculations. The versatile function of substrate 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX) is explored in this study. In the [Cp*RhCl 2 ] 2 -catalyzed reaction, TIPS-EBX is acted as the Brønsted base to go through the self-assisted deprotonation mechanism to produce the C8alkynylation product solely. The obvious regioselectivity could be attributed to the electron effects. In contrast, due to the steric effects, the C4-alkynylation product becomes the major product by employing AuCl as the catalyst. In this reaction, the iodine(III) center in the TIPS-EBX moiety could be employed as a strong Lewis acid to activate the alkyne moiety efficiently.

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Am echanistic study of the Cp*Rh III -catalyzed (Cp* = h 5 -pentamethylcyclopentadienyl) intramolecular redox-neutral annulation of tethered alkynes was carried out by density functional calculations using the M06 method. Our results show that the reductive elimination step of the catalytic cycle is rate determining, and the overall energy barrier of the entire process is 31.4 kcal mol À1 (L-II!L-TS8-9). This is in agreement with experimental resultst hat re-portedt he CÀHb ond cleavage not to be the rate-determining step. According to our calculations,t he feasible mechanism for the Rh III !Rh V !Rh III process involves an acylamino migration and subsequent reductive elimination process, which is different from the pathwayp reviously proposed by Li's group.T he present calculations elucidate the experimental observations on the molecular level.[a] W.Scheme1.Rh III -catalyzed intramolecular redox-neutral annulationo fa lkyne-tethered phenylhydrazinea ccording to Li and co-workers. [20] Scheme2.Plausible pathway proposed by Li and co-workers [20] for the Rh III -catalyzed intramolecular redox-neutral annulation of alkyne-tetheredp henylhydrazine.

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