965-85-5Relevant academic research and scientific papers
Excited- and ground-state versions of the tri-π-methane rearrangement: Mechanistic and exploratory organic photochemistry
Zimmerman,Cirkva
, p. 1839 - 1851 (2007/10/03)
The di-π-methane rearrangement with two π-groups bonded to a single carbon leading to π-substituted cyclopropanes is now well established. The present research had as its goal the exploration of molecular systems having three π-moieties attached to an sp3-hybridized atom in a search for a tri-π-methane rearrangement. Indeed, it was found that such systems do rearrange photochemically to afford cyclopentenes. However, it was also established that vinylcyclopropanes ring-expand to cyclopentenes on direct irradiation. Since both three-ring and five-ring photoproducts often are found to be produced, it was important to establish that the observed photochemistry was really the result of a true single-step tri-π-methane rearrangement and not the consequence of two sequential rearrangements, first to form a vinyl cyclopropane which subsequently ring expanded to the cyclopentene. The general situation has three species - A, B, and C - corresponding to tri-π-methane reactant A, vinylcyclopropane photoproduct B, and cyclopentene photoproduct C. Three rate constants are involved, k1 for A → B, k2 for A → C, and k3 for B → C. The kinetics were applied to two examples with provision to avoid differential light absorption; this utilized singlet sensitization. It was determined that direct formation of the cyclopentene photoproduct proceeds more rapidly than the ring-expansion route. In contrast to the di-π-methane rearrangement, the tri-π-methane reaction was found to be preferred by the singlet, while in these sterically congested systems; the triplet led to di-π-methane reactivity. Finally, a ground-state counterpart of the reaction was obtained.
New Host Family Based on Small-Ring Compounds
Weber, Edwin,Hecker, Manfred,Csoeregh, Ingeborg,Czugler, Matyas
, p. 7866 - 7872 (2007/10/02)
Three- and four-membered ring compounds with functional groups and bulky substituents have proved to be a rewarding new source of inclusion hosts.These hosts form clathrates with a variety of uncharged organic molecules ranging from protic dipolar to apolar compounds (168 different inclusion species).Formation and selectivity depend in a systematic manner on structural parameters of the host, such as the nature, number, and position of functional groups, the substituents, and ring size.X-ray structure analyses of two inclusion compounds 12121; = 9.782 (1), b = 11.376 (1), c = 17.603 (1) Angstroem; Z = 4. 17*MeCN (1:1): Pbcn; a = 12.314 (1), b = 16.074 (1), c = 12.938 (1) Angstroem; Z = 4> and of a free host molecule 1; a = 7.339 (2), b = 11.657 (4), c = 9.149 (3) Angstroem; β = 110.070; Z = 2> are reported, revealing the building principles of the new clathrate family.The structures exhibit linear chains of inter-/intramolecular H bridges between carboxylic groups in the free host 1 and H-bridge aggregation of host and guest molecules in infinite helical chains for the 1*t-BuOH (1:1) inclusion.In 17*MeCN (1:1), the guest molecules are tightly enclosed by the host framework without further specific interactions.
