1,3‐Dipolar Cycloadditions to Strained Olefins

Abstract

Abstract The Bredt olefins bicyclo [3.3.1]non‐1‐ene (2) , bicyclo [4.2.1]non‐1 (8)‐ene (3) , and bicyclo [4.2.1]non‐1 (2)‐ene (4) react rapidly with 1,3‐dipoles such as diazomethane, phenyl azide, and mesitonitrile oxide to yield mixtures of two regioisomeric cycloadducts 10, 11 and 12 , respectively. On the contrary, cycloaddition to the comparable monocyclic 1‐methyl‐( E )‐cyclooctene (5) is fairly regioselective. 2‐Methylnorborn‐2‐ene (6) gives one isomer with mesitonitrile oxide (as do less strained olefins), but mixtures with diazomethane and phenyl azide. 1 H‐NMR. and 13 C‐NMR. spectra of the cycloadducts are reported. The results are discussed in the light of frontier molecular orbital theory.