The titanium-catalyzed 3-component coupling of an alkyne, isonitrile, and amine can be used to generate tautomers of 1,3-diimines. These di-A C H T U N G T R E N N U N G imines produced in situ undergo cyclization with hydrazine and hydrazine derivatives in a one-pot procedure to provide pyrazoles. Seventeen examples of pyrazoles are provided using this one-pot, 4-component procedure from simple starting materials. The regioselectivity of the alkyne addition can be controlled in some cases with catalyst architecture, and regioselectivity of monosubsituted hydrazines to unsymmetrical 1,3-diimines is discussed. This multicomponent coupling strategy was applied to the synthesis of withasomnine in an efficient procedure, which gave the natural product in 24% overall yield from 4-pentyn-1-ol.
A titanium-catalyzed three-component coupling reaction can be used to generate tautomers of N-aryl-1,3-diimines. Simple treatment of these products with acetic acid leads to cyclization forming quinoline derivatives in a one-pot procedure. The primary amines employed can be substituted anilines, aminonaphthalenes, or even heterocyclic amines, which leads to a variety of fused-ring heterocyclic frameworks. The one-pot yields varied from 25-71% for the 18 examples presented in this study.
A general and efficient synthesis of imidazo[2,1-a]phthalazines by palladium-and copper-mediated coupling of N-aminoimidazoles with 2-haloaryl aldehydes with concurrent imine formation is described. This new synthesis of the imidazo[2,1-a]phthalazine ring system allows for facile introduction of different substituents around the entire core.
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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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