Effect of increasing electron demand upon the product-determining transition state in the reaction of 4-substituted 2-nitrobenzenesulfenyl chlorides and benzenesulfenyl chlorides with bicyclo[2.2.1]hepta-2,5-diene

1979 ◽  
Vol 44 (20) ◽  
pp. 3555-3559 ◽  
Author(s):  
Dennis G. Garratt ◽  
Pierre L. Beaulieu
Keyword(s):  
Transition State ◽  
Electron Demand

Electrophilic cleavage of cyclopropanes. II. Concerning the effect of increasing electron demand upon the product-determining transition state in the reaction of 4-substituted-2-nitrobenzenesulphenyl chlorides and benzenesulphenyl chlorides with tetracyclo[3.2.0.02,7.04,6]heptane (quadricyclene)

1980 ◽  
Vol 58 (10) ◽  
pp. 1014-1020 ◽  
Author(s):  
Pierre L. Beaulieu ◽  
Ann Kabo ◽  
Dennis G. Garratt
Keyword(s):  
Transition State ◽  
Nitro Group ◽  
Phenyl Ring ◽  
Relative Proportion ◽  
Electron Demand

The effect of increasing electron demand upon the product-determining transition state in the reaction of arenesulphenyl chlorides with tetracyclo[3.2.0.02,7.04,6]heptane has been investigated. As the electron donating ability of the remote substituents on the phenyl ring of the sulphenyl chloride is varied from nitro to methoxy the relative proportion of adducts derived from edge-on attack is found to increase relative to that of adducts derived from corner attack. An ortho-nitro group was found to lead to a stabilizing interaction only in the case of 2,4-dinitrobenzenesulphenyl chloride. A mechanism involving the competition between the two conceptual modes of approach is suggested.

scholarly journals Anchimeric Assistance in Hydrogen-Atom Transfer to Bromine

2004 ◽  
Vol 57 (7) ◽  
pp. 651 ◽  
Author(s):  
Anna K. Croft ◽  
Christopher J. Easton
Keyword(s):  
Free Radical ◽  
Hydrogen Atom ◽  
Transition State ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Rate Enhancement ◽  
Anchimeric Assistance ◽  
Electron Donation ◽  
Electron Demand

The free-radical benzylic brominations of series of phenylalanine derivatives and O-phenylalkyl benzoates and N-phenylalkylamides with N-bromosuccinimide exhibit anchimeric assistance by neighbouring ester and amido groups. Rate enhancement occurs through electron donation to the electropositive carbon centre that develops in the transition state of the hydrogen-atom transfer to bromine. The extent of the effect depends on the electron demand at the benzylic position and the electron-donating ability of the neighbouring group.

Memapsin 2, a drug target for Alzheimer's disease

2003 ◽  
Vol 70 ◽  
pp. 213-220 ◽  
Author(s):  
Gerald Koelsch ◽  
Robert T. Turner ◽  
Lin Hong ◽  
Arun K. Ghosh ◽  
Jordan Tang
Keyword(s):  
Crystal Structure ◽  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Transition State ◽  
Amyloid Precursor Protein ◽  
Therapeutic Target ◽  
Drug Target ◽  
Aspartic Protease ◽  
Precursor Protein ◽  
Memapsin 2

Mempasin 2, a ϐ-secretase, is the membrane-anchored aspartic protease that initiates the cleavage of amyloid precursor protein leading to the production of ϐ-amyloid and the onset of Alzheimer's disease. Thus memapsin 2 is a major therapeutic target for the development of inhibitor drugs for the disease. Many biochemical tools, such as the specificity and crystal structure, have been established and have led to the design of potent and relatively small transition-state inhibitors. Although developing a clinically viable mempasin 2 inhibitor remains challenging, progress to date renders hope that memapsin 2 inhibitors may ultimately be useful for therapeutic reduction of ϐ-amyloid.

Collisional dynamics of Ca1D + HBr reactions: evidence for transition-state motions

1999 ◽  
Vol 97 (8) ◽  
pp. 967-976 ◽  
Author(s):  
M. Garay Salazar, J. M. Orea Rocha, A.
Keyword(s):  
Transition State ◽  
Collisional Dynamics

Reactions of an Aluminium(I) Reagent with 1,2-, 1,3- and 1,5-Dienes: Dearomatisation, Reversibility, and a Pericyclic Mechanism

2019 ◽  
Author(s):  
Clare Bakewell ◽  
Martí Garçon ◽  
Richard Y Kong ◽  
Louisa O'Hare ◽  
Andrew J. P. White ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Dft Calculations ◽  
Transition State ◽  
Reaction Pathways ◽  
Aromatic Rings ◽  
Aromatic Character ◽  
Pericyclic Reaction

The reactions of an aluminium(I) reagent with a series of 1,2-, 1,3- and 1,5-dienes are reported. In the case of 1,3-dienes the reaction occurs by a pericyclic reaction mechanism, specifically a cheletropic cycloaddition, to form aluminocyclopentene containing products. This mechanism has been interrogated by stereochemical experiments and DFT calculations. The stereochemical experiments show that the (4+1) cycloaddition follows a suprafacial topology, while calculations support a concerted albeit asynchronous pathway in which the transition state demonstrates aromatic character. Remarkably, the substrate scope of the (4+1) cycloaddition includes dienes that are either in part, or entirely, contained within aromatic rings. In these cases, reactions occur with dearomatisation of the substrate and can be reversible. In the case of 1,2- or 1,5-dienes complementary reactivity is observed; the orthogonal nature of the C=C π-bonds (1,2-diene) and the homoconjugated system (1,5-diene) both disfavour a (4+1) cycloaddition. Rather, reaction pathways are determined by an initial (2+1) cycloaddition to form an aluminocyclopropane intermediate which can in turn undergo insertion of a further C=C π-bond leading to complex organometallic products that incorporate fused hydrocarbon rings.

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