1,3-DIPOLAR CYCLOADDITIONS TO STRAINED OLEFINS

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. 1H‐NMR. and 13C‐NMR. spectra of the cycloadducts are reported. The results are discussed in the light of frontier molecular orbital theory. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim