Rearrangement computational studies

Cope and Sila-Cope Rearrangements Computational studies by Yates et ed. on 1,5-enynes were used to rationalize the different regioselectivities observed for the Au(I)-catalyzed addition of alcohols to the all carbon (X = C) and silyl 1,5-enynes (X = Si) as shown in Eq. (5.9) [35]. 

The focus of the next four chapters (Chapters 14-17) is mainly on the theoretical/computational aspects. Chapter 14 by T. S. Sorensen and E. C. F. Yang examines the involvement of p-hydrido cation intermediates in the context of the industrially important heptane to toluene dehydrocyclization process. Chapter 15 by P. M. Esteves et al. is devoted to theoretical studies of carbonium ions. Chapter 16 by G. L. Borosky and K. K. Laali presents a computational study on aza-PAH carbocations as models for the oxidized metabolites of Aza-PAHs. Chapter 17 by S. C. Ammal and H. Yamataka examines the borderline Beckmann rearrangement-fragmentation mechanism and explores the influence of carbocation stability on the reaction mechanism. 

A recent study has indicated that the skeletal rearrangement step in the B12-catalysed isomerization of methylmalonyl-CoA to succinyl-CoA occurs not by a radical pathway but by an anionic or organocobalt pathway. A computational study of the isomerization of allyl alcohol into homoallyl alcohol by lithium amide has pointed to a process proceeding via a transition state in which the proton is half transferred between carbon and nitrogen in a hetero-dimer. l,l-Dilithio-2,2-diphenylethene... 

Computational studies of the CH3CCI to vinyl chloride rearrangement (Scheme 7.17) provide an activation energy that can be compared to those measured by LFP experiments.The gas phase computed a is 11.5 kcal/ mol, which is reduced to 9.3 kcal/mol in (simulated) heptane." The experimental value in isooctane is 4.9 kcal/mol. Some of the 4.4 kcal/mol difference between the computed and observed a can be narrowed if quantum mechanical tunneling (QMT) is included in the calculations The migrant H atom can tunnel through the activation barrier as well as chmb over The... 

The oldest reaction involving a rearrangement of an organozinc compound is probably the Reformatsky reaction54 55. It took one hundred years until its key step could be classified as a [3,3)-sigmatropic shift ( metallo-Claisen rearrangement) on the basis of computational studies (equation 51)56. 

Unusual cationic species, e.g. nonclassical bicyclobutonium ions, are discernible in the solvolytic rearrangements, depending on the structure of the substrate.3,4 Computational studies using ab initio at the STO 4-31G level of theory indicate that the molecular symmetry of the unsubstituted parent cation C4H, is a bisected form of the cyclopropylmethyl system.5... 

A computational study has been carried out593 on the rearrangement reactions of methylsilacyclopropane, and the pathway shown in Scheme 118 has been put forward594 to account for the formation of product (459) from the reaction of Me2AlCl with the (2 + 2)-cycloadduct (458) between naphthoquinone and allyl trimethylsilane. 

Experimental and computational studies of the pericyclic Meisenheimer rearrangement and a competitive rearrangement of A-propargyl morphol i nc N-oxide revealed a novel inverse secondary kinetic isotope effect (kn/kD 0.8) for the rate-determining cyclization step, probably occurring because of a C(sp) to C(sp2) change in hybridization at the reaction center (Scheme 3).5... 

Despite enormous strain, cubane is kinetically stable because breaking just one C—C bond causes only minor structural changes and hence only little relief of strain. A computational study shows that protonation occurs to give edge-protonated cubane.28 Cleavage of a second C—C bond is highly exothermic and this is followed by a further series of rapid exothermic molecular rearrangements (Scheme 16). 

The preference for a chairlike transition state in the Johnson-Claisen rearrangement is supported by further Houk et al. s computational studies (Scheme 1.2e).5 For the rearrangement of the parent methyl ketene acetal, chairlike transition state A is favored over boatlike transition state B by 2.3 kcal/mol. 

Formyl and 2-acetylfuran underwent an unusual reaction with ethyl azodicarboxylate to form adducts 285 and 286, respectively, as depicted in Equation (177) <1997T9313, 1999J(P1)73>. Computational studies of the reaction suggested an initial Diels-Alder reaction between the furan and azodicarboxylate, followed by rearrangement of the cycloadducts. A similar transformation was observed for the reaction between furfurals and 1,4-phthalazinedione in the presence of Pb(OAc)4, as shown in Equation (178) <20020L773>. 

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