Showing papers on "Intramolecular reaction published in 1976"

Computer Simulation of the Intramolecular Reaction of Polymers

Abstract: A computer simulation is made for the intramolecular reaction of a flexible polymer chain. The reaction rate k1 is obtained for various values of the degree of polymerization and the size of the reaction region. Previous theories for the intramolecular reaction rates are examined by a comparison with these results.

Photoinduced transformations. Part XXX. Photorearrangement of (22S,25S)-N-acetylveratra-5,8,13(17)-trienine-3β,11β,23β-triol 3,23-diacetate 11-nitrite, a fused cyclopentenyl nitrite, to two spiroisoxazolines

Abstract: Irradiation of the title nitrite (3) in protic or aprotic solvents with Pyrex-filtered light induced an extensive rearrangement to afford two products with novel isoxazoline structures, designated photo-TVTTN and isophoto-TVTTN, in good yields. The structure and absolute configuration of photo-TVTTN (4) were determined by chemical and spectroscopic studies and by an X-ray crystallographic analysis of an iodine-containing derivative (14). The structure and absolute configuration of isophoto-TVTTN (5) were deduced by spectroscopic studies.A photoreaction carried out with monochromatic light (362 ± 4 nm) confirmed that light was only involved in homolysis of the O–NO bond, and that photo- and isophoto-TVTTN were formed via an unstable hydroxyimino-aldehyde (19), which was isolated. The hydroxyimino-aldehyde was transformed smoothly into photo- and isophoto-TVTTN on silica gel during t.l.c. Whereas the silica gel-induced transformation was non-stereoselective, leading to both photo-(4) and isophoto-TVTTN (5), the transformation of the hydroxyimino-aldehyde with acetic acid or [2H]acid was stereoselective, giving mainly isophoto-TVTTN (5) or [9β-2H]isophoto-TVTTN (21), respectively. Deuterium is incorporated into the TVTTNs in the course of intramolecular Michael reaction catalysed by acetic [2H]acid. This unusually ready intramolecular reaction seems to be the first reported example of a Michael addition of an oxime hydroxy-group to an αβ-unsaturated carbonyl system.