Cyclopropanation computational studies

A computational study of cyclopropanation reactions of the divalent samarium carbenoid ISmCH2I with ethylene has been presented. The ISmCH2I species was found to have a samarium carbene complex character with... 

Abstract The application of QM/MM methods to the study of the reaction mechanisms involved in chemo-, regio-, and enantio- selective processes has been a very productive area of research in the last two decades. This review summarizes basic general ideas in both QM/MM methods and the computational study of selectivity and presents selected results on the study of three of the most representative examples of these applications rhodium-catalyzed hydrogenation, rhodium-catalyzed hydroformylation, and copper-catalyzed cyclopropanation. 

Computational studies of the carbenoid cyclopropanation reactions of methoxymethyl-lithium and intra- and intermolecular carbenoid reactions of lithiated oxiranes have been reported. Computations suggest that methoxymethyllithium reacts with ethylene exclusively by a stepwise carbolithiation mechanism. The intramolecular reaction of lithiated l,2-epoxy-5-hexene was found to proceed by both the carbohthiation and the methylene transfer pathways, but the former is expected to dominate at room and low temperatures because the free energy of activation is less than half that of the latter pathway. 

The discussion of the catalytic, asymmetric variants will incorporate a significant emphasis on the interplay of mechanistic investigations and synthetic optimization studies to provide a unified picture of the cyclopropanation methods. Finally, recent insights provided by computational analysis of the transition structures for cyclopropanation will be discussed. 

Let us now consider tetrahedrane 6 and [l.l.l]propellane 7. Both species have numerous 3MRs or cyclopropane rings. We thus expect both compounds to be highly strained. Do these hydrocarbons belong to anv homologous series Are they to be understood as avatars for the study of yet more wondrous strained species Are they, as it were, alicycles resplendent in glorious isolation despite the considerable attention paid to both tetrahedrane [27] and [l.l.l]propellane [28] by computationally oriented theoretical chemists ... 

Computer s investigation of the chemical data bases (Chemical Abstracts) covering the period 1966-1984, dealing with the term CYCLOPROP (for cyclopropane and (or) cyclopropyl) gave 10 799 items. Consequently, only the main features of this topic are discussed in order to show the considerable efforts which have been and which are still currently devoted to the study of the challenging cyclopropane chemistry. 

Zhao, C., Wang, D.-Q., Phillips, D. L. Density functional study of selected mono-zinc and gem-dizinc radical carbenoid cyclopropanation reactions observation of an efficient radical zinc carbenoid cyclopropanation reaction and the influence of the leaving group on ring closure. Journal of Theoretical Computational Chemistry 2003, 2, 357-369. 

Substrate probes have aided mechanistic understanding of the key C— H activation step in the MMOH reaction cycle. Chiral alkanes and radical-clock substrate probes " " were used to discriminate between radical recoil/rebound and nonsynchronous concerted insertion pathways. A short lifetime (< 150 fs) estimated for the putative radical species derived from cyclopropane-based radical-clock substrates favors the latter process,whereas partial racemization of chiral ethane substrate is consistent with the former scenario. A unifying model was proposed, in which both recoil/rebound and concerted reaction channels are available for a bound radical intermediate and the partitioning between each trajectory is dependent on the substrate. Formation of carboca-tion-derived products from certain probes implicates yet another route involving a formal OH+ insertion.Participation of multiple species capable of oxygen transfer is an emerging mechanistic view in both heme and nonheme systems, as exemplified by the studies of cP450s and their synthetic models.Scheme 3 depicts various density functional theory (DFT) models of MMOHq and their computed reaction pathways, which are reviewed in detail elsewhere. 

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