Abstract
N-O heterocycle compounds play an important role in various fields. Doyle et al. (Cheng et al., 2017) have recently reported an efficient catalyst-controlled selective cyclization reactions of tert-butyldimethylsilyl (TBS)-protected enoldiazoacetamides with nitrosoarenes in which the multifunctionalized products 5-isoxazolones and 1,3-oxazin-4-ones were formed through [3+2]- and [5+1]-cyclizations using Rh2(oct)4 and Rh2(cap)4 as catalysts, respectively. The present work studied the mechanism of the reactions in question and the origins of the catalyst-dependent chemoselectivity by the density functional theory (DFT) calculations at the M06-D3/SMD/6-311+G(d,p)//B3LYP-D3/6-31G(d,p) level of theory. The computed results illustrate the importance of the different dirhodium catalysts to gain diversified N-O heterocycle compounds and suggest the specific interaction between the reactants by the real catalyst model. Meanwhile, it is the steric hindrance and electronic effect of the ligands of dirhodium catalysts that control the reaction mechanism. Furthermore, the other auxiliary theoretical analysis, natural bond orbital calculation and distortion/interaction analysis, make the electronic effects, and steric hindrance more distinct.
Highlights
Diazo compounds play a significant role in organic synthetic field, and these compounds are always classified as three typical classes: acceptor, donor/acceptor, and acceptor/acceptor, according to the electronic effect of the substituents (Davies and Beckwith, 2003; Zhu et al, 2008), as shown in Scheme 1
We first studied the [3+2]-cycloaddition reaction catalyzed by Rh2(OAc)4, for which the following mechanisms were hypothesized according to our previous study and the mechanism provided by the experimental author (Cheng et al, 2017), as shown in Scheme 4
It’s worth mentioning that this cyclopropene 3 was detected in the [3+2]-cycloaddition process of Rh2(OAc)4catalyzed diazo compound as the intermediate (Cheng et al, 2017), the reaction mechanism must go through this step
Summary
Diazo compounds play a significant role in organic synthetic field, and these compounds are always classified as three typical classes: acceptor, donor/acceptor, and acceptor/acceptor, according to the electronic effect of the substituents (Davies and Beckwith, 2003; Zhu et al, 2008), as shown in Scheme 1. Based on our previous research, we are interested in the reactions catalyzed by divergent dirhodium catalysts reported by Dolye group (Cheng et al, 2017) In their experiments (shown in Scheme 3), they detected the presence of certain intermediates, but the mechanism remained unclear. BS2 denotes a mixed basis set of 6-311+G(d,p) for all non-metal elements and [Stuttgart RSC 1997 ECP+4f] for rhodium atom These M06-D3/SMD/BS2 electronic energies were added to the free energy correction evaluated from the unscaled vibrational frequencies on the B3LYP-D3/BS1 optimized geometries in the gas phase at 298.15 K and 1 atm to obtain the Gibbs free energies in chloroform solvent. Interaction (NCIplot) analysis was carried out with program Multiwfn (Lu and Chen, 2012)
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