The first crystal structure t o be determined for an inclusion complex in which a chemically modified cyclodextrin serves as the host reveals a host molecular conformation that retains many of the features of the parent molecule but provides an extended toroidal region in which larger hydrophobic substrate molecules can be accommodated.
Verschiedene y-Brom-P-oxonitrile 3 reagieren in Gegenwart von Silberoxid rnit Furan stereoselektiv zu den Titelverbindungen 7. Befriedigende Ausbeuten werden nur mit solchen Bromiden 3 erhalten, deren y-Kohlenstoff tertiar ist oder die sowohl am a-als auch y-Kohlenstoff monoalky- Some y-bromo-0-oxonitriles 3 react with furan in the presence of silver oxide to form stereoselectively the title compounds 7. Satisfying yields are obtained only with those bromides 3, whose y-carbon ist tertiary or which are monoalkylated both at the a-and y-carbon atoms. The results are explained by a [4 + 31 cycloaddition of 1-cyanoallylium-2-olate intermediates (14) to the 1,3-diene system of the furan. With cyclic y-bromo-p-oxonitriles (6) two types of cycloadducts were observed: 3-bromo-3-methyl-2-oxocyclohexanecarbonitrile (6b) and 3-bromo-2-oxocyclododecanecarbonitrile (6d) form the tricyclic (4 + 31 cycloadducts 10b and d, analogs of the bicyclic adducts 7. With 3-bromo-2-oxocyclohexanecarbonitrile (6 a) and 3-bromo-5-terf-butyl-2-oxocyclohexanecarbonitrile (6e), however, the carbonyl oxygen is connected with an a-carbon of the furan to give the tricyclic [3 + 21 cycloadducts 12Aa and Ae. The structure of endo-2,endo-4-dimethyl-3-oxo-8-oxabicyclo[3.2.l]oct-6-ene-exo-2-carbonitrile (7ea) was determined by X-ray analysis.
~~Die reduktive Enthalogenierung von a, a'-Dibromketonen in Gegenwart von 1,3-Dienen hat einen eleganten Weg zu Cycloheptenonen e~-Offnet~*~). Als reaktive Zwischenstufen werden Allylium-2-olate -meist als ,,Oxallyle" bezeic%et -und 2-Hydroxyallyl-Kationen angenommen, welche mit dem 1,3-Dien in einer [4 + 31-Cycloaddition reagieren 6).
A crystal structure determination for Tyr-o-Nle-Gly-Phe-NIeS [NleS = MeCH2CH2CH2CH(NH2)S03H] provides t w o examples of a 2'-P-bend conformation for a biologically active, synthetic enkephalin analogue.
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