1,3-Dipolar cycloadditions to bicyclic olefins. V. The stereo- and regiochemistry of 1,3-dipolar cycloadditions to several unsymmetrical bicyclic olefins.

Each of the 1,3-dipolar cycloadditions of phenylglyoxylonitrile oxide (1), methylglyoxylonitrile oxide (2), benzonitrile oxide (3), and phenyl azide to 2-phenylsulfonyl-2-azabicyclo[3.2.1]octa-3,6-diene (6) occurs only to the C6–C7 double bond, affording two exo regioisomers. Each of the cycloadditions of 1, 2, and 3 to 2-phenylsulfonyl-2-azabicyclo[3.2.1]oct-3-ene (7) gives only one exo adduct. The cycloaddition of C,N-diphenylnitrone to 2-methylenenorbornane (8) gives a mixture of two exo adducts. These results show that the “exo rule” can be extended to the 1,3-dipolar cycloadditions to the bicyclic olefins, 6, 7, and 8. Tentative explanations are offered to account for the exo stereoselectivity and the regio-selectivity in these cycloadditions.