Cyclic 2-diazo-1,3-dicarbonyl compounds react with diketene in the presence of rhodium(II) salts to give benzofurans as the major isolated products. The formation of intermediate products with exocyclic double bonds which isomerise to benzofurans provides support for the proposed mechanism which involves initial formation of a dioxaspirooctenone by a formal dipolar cycloaddition reaction of a carbenoid to the exocyclic double bond of diketene followed by the loss of carbon dioxide. Acyclic 2-diazo-1,3-dicarbonyl compounds give furans in poor yield.
环状 2-重氮-1,3-二羰基化合物在
铑(II)盐存在下与二酮反应,生成的主要分离产物是
苯并呋喃。中间产物的外环双键异构化为
苯并呋喃,这为所提出的机理提供了支持,即通过类羰基化合物与二酮烯的外环双键发生形式上的二极环加成反应,最初形成二噁螺辛酮,随后
二氧化碳流失。环状 2-重氮-1,3-二羰基化合物生成
呋喃的产量很低。