Saturated heterocycles 115: Cycloaddition of nitrilimine and nitrile oxide to norbornane- and norbornene-fused dihydro-1,3-oxazines

Abstract

By cycloaddition of nitrilimine and nitrile oxide to diexo and diendo norbornane- and norbornene-fused structural isomeric dihydro-1,3-oxazlnes ( 1- 3), tetracyclic 1,3-oxazino-1, 2,4-trlazolines ( 7- 9) and 1,2,4-oxadiazolines ( 10- 12) were obtained. With norbornehe dipolarophiles, which contain a C=N and a C=C bond, the cycloaddition takes place at the olefinic bond and the diexo compound 4 yields 13 regioselectively, whereas the diendo isomer 5 gives an Isomeric mixture of isoxazolines 14 and 15. From the diexo derivative 6, however, a bis-adduct 16 is formed. The stereostructures of the adducts have been elucidated by NMR spectroscopy.