Ketene Equivalent

Generally, ketenes react with conjugate dienes by [2+2] cycloaddition so that the Diels-Alder adducts are not obtained. The reagent 1 is a ketene equivalent that undergoes the Diels-Alder reaction with a variety of dienes. For example, 1 reacts thermally with cyclopentadiene to yield a cycloadduct which upon treatment with base produces norbornenone^1a). Furthermore, 1 also reacts with substitute furanes and this reaction has been used for the synthesis of sesquiterpene which is a family of biologically active natural products^1b).