Reactions of Activated Enynes with Diazomethane
Electron-deficient conjugated enynes interact with diazomethane under mild conditions at the double bond with formation of the corresponding nitrogen-containing cycloadducts or cyclopropanes. The structure of the products of these reactions depends on the number of acceptor groups at the double bond of the starting enyne: 1,5-diarylpent-2-en-4-yn-1-ones form 2-pyrazolines, propargylidenemalonic acid esters - 1-pyrazolines, and the enyne derivatives of Meldrum’s acid - 5,7-dioxaspiro[2.5]octane-4,8-diones. Non-catalytic methods have been developed for the preparation of spirocyclic cyclopropanes and ethynyl-substituted 1- and 2-pyrazolines with 75-90% yields.