Dipolar cycloaddition reactions of diazoindene and the thermal behavior of the cycloadducts

A study of the dipolar cycloaddition behavior of diazoindene toward electron-deficient acetylenic and olefinic dipolarophiles has been carried out. Reactions with alkynes afford transient 1,3-dipolar cycloadducts. Product formation can be attributed to a substituent-dependent partitioning between spiro 3H-pyrazole adducts and ring opened diazoalkenes. The initially formed cycloadducts lose nitrogen to give a spirocyclopropene derivative or undergo the van Alphen – Huttel rearrangement. When olefinic dipolarophiles are used, nitrogen deficient 1:1 adducts are isolated. The formation of the product involves the further loss of nitrogen from the initially formed spiropyrazoline adduct.