Vinylcarbenes acycliques: reactions de cycloadditions intermoleculaires

Article abstract of DOI:10.1016/0040-4020(78)88422-1

The photolysis of 3,3-dimethyl-3H-pyrazoles in unsaturated solvents leads in good yields and often with high stereoselectivity, to vinylcarbene cycloadducts. This direct synthesis of vinylcyclopropanes, vinylcyclopropenes and divinylcyclopropanes shows that acyclic vinyl carbenes are not necessarily intramolecularly stabilized. They can actually be trapped by olefins, acetylenes or dienes, depending on the carbene substituents. Cyano vinyl carbenes are the most efficient intermolecular cycloaddenda examined so far, but carbalkoxy and even ketovinylcarbenes can undergo cyclopropanation reactions with dienes, with little competition from the Wolff rearrangement in the last case.