114789-92-3Relevant academic research and scientific papers
Photochemistry in a crystalline cage. Control of the Type-B bicyclic reaction course: Mechanistic and exploratory organic photochemistry
Zimmerman,Sebek
, p. 3677 - 3690 (2007/10/03)
Our current theories on crystal lattice control of organic photochemistry were subjected to studies of type-B rearrangement of bicyclo[3.1.0]hex-3-en-2-ones. A first finding was that the solid state photochemistry differed dramatically from that in solution. One of our past observations in this bicyclic photochemistry in solution was that the six-membered ring, type B, zwitterion was a ubiquitous intermediate. This intermediate invariably underwent a preferential migration of an aryl group to carbon-2 relative to carbon-4 with formation of a 2,3-disubstituted phenol, a result deriving from electronic effects. In contrast, the crystal lattice photochemistry revealed a regioselectivity depending on the surrounding lattice rather than electronics. Perhaps an even more dramatic difference was an observation of the dependence of reactant stereochemistry. Thus, in solution, for 6,6-disubstituted bicyclics with two different groups at C-6, a common zwitterion is formed and the same photoproduct is formed independent of reactant stereochemistry. In crystal lattices the endo and exo stereoisomers of the 6,6-disubstituted bicyclics react differently and the group originally endo tends to migrate after three-ring opening to the zwitterion. The experimental results were paralleled with a theoretical analysis. This consisted of generation of a 'mini crystal lattice' with sufficient lattice molecules to completely surround a central, reacting electronically excited state molecule. Then computational extraction of the central molecule and replacement by a transition structure afford a model of the reacting excited state inside the crystal lattice. Overlap of this species with the lattice neighbors and energy computations are then possible. These permit prediction and understanding of excited state crystal lattice reactivity on a quantitative basis.
Cyclopropanols and the Di-?-methane Rearrangement: Mechanistic and Exploratory Organic Photochemistry
Zimmerman, Howard E.,Nuss, John M.,Tantillo, Anthony W.
, p. 3792 - 3803 (2007/10/02)
The photochemistry of a series of di-?-methane systems, having a hydroxyl group on the methane carbon, was investigated.Both the divinyl and the aryl vinyl versions were studied.In certain cases, an isomeric γ,δ-unsaturated ketone was obtained; the reactant a-b-c-d-e carbon skeletal sequence was permuted to afford the product with the sequence c-a-b-d-e.In two cases intermediate cyclopropanols could be isolated and in all instances evidence was obtained that the bizarre rearrangement resulted from a di-?-methane rearrangement followed by ring opening of the resultant cyclopropanol.Photolysis of the corresponding phenyldimethylsilyl ethers led nicely to the corresponding cyclopropyl ethers in all cases.Tetrabutylammonium fluoride treatment resulted in ring opening.Quantum yields and reaction multiplicites were determined.Direct and sensitized irradiations established both singlet and triplet reactivity.The photochemistry of the cyclopropane products revealed cis-trans isomerization of the silyl ethers and, additionally, ring opening of the cyclopropanols.One of the reactions proved reversible, thus 1,2,2,5,5-pentaphenylpent-4-en-1-one afforded the stereoisomeric 1,2,2-triphenyl-3-cyclopropanols.Single photon counting was employed to obtain the excited singlet lifetime and reaction rate for 1,1,3,3-tetraphenyl-2-propen-1-ol.
