通过碱介导的1,3-二羰基向2-硝基苯并呋喃的迈克尔加成反应,然后分子内环化,已经实现了合成二氢呋喃[2,3- b ]苯并呋喃衍生物的简单方法。各种1,3-二羰基化合物,包括环状的以及三氟甲基化的,都已在最佳条件下与2-硝基苯并呋喃进行了反应,相应的二氢呋喃[2,3- b ]苯并呋喃的回收率中等至优异。 。
Dipolar cycloaddition of cyclic rhodium carbenoids to aromatic heterocycles
作者:Michael C. Pirrung、Jiancun Zhang、Andrew T. McPhail
DOI:10.1021/jo00022a010
日期:1991.10
Cyclic diazo 1,3-dicarbonyl compounds are decomposed by rhodium carboxylate salts in the presence of furans, dihydrofurans, pyrroles, and indoles to generate 7-oxatricyclo[6.4.0.0(2,6)]dodecane derivatives.
Reactions of a Cyclic Rhodium Carbenoid with Aromatic Compounds and Vinyl Ethers
作者:Michael C. Pirrung、Jiancun Zhang、Karen Lackey、Daniel D. Sternbach、Frank Brown
DOI:10.1021/jo00112a036
日期:1995.4
Further investigation has been made of the reactions between the cyclic diazo compound 2-diazo-1,3-cyclohexanedione and aromatic heterocycles or vinyl ethers, catalyzed by rhodium carboxylates. The extraordinary reactivity of the carbenoid derived from this diazo compound is shown by its ready reaction with solvents such as dichloromethane, dichloroethane, and fluorobenzene. Detailed investigation of its reactions with furans have shown that steric interactions dominate, both in terms of regioselectivity with unsymmetrical substrates and yield. This reaction provides a useful entry to the furo[2,3-b]furan ring system found in a number of naturally-occurring compounds and is formally a 1,3-dipolar cycloaddition. Products of net C-H insertion and with reverse regiochemistry (furo[3,2-b]furan ring system) were also detected. With pyrroles and thiophenes, cycloadducts were seen in a few cases, but were generally the exception; C-H insertion products dominate these reactions. Vinyl ethers proved reliable reactants in providing dipolar cycloadducts. The results of this study have been interpreted in terms of four pathways: an initial cyclopropanation would produce a spirocyclic dicarbonyl system that on heterolytic cleavage of one of the two cyclopropane bonds would give a zwitterion. The partitioning of such a zwitterion between ring closure and proton transfer would define the ratio of C-H insertion and dipolar cycloaddition products. Both thermodynamic and stereoelectronic arguments have been advanced to explain the observations and were supported by calculations.