The relative reactivities of ‘normal’ and angle strained cyclo-olefins in 1,3-dipolar cycloaddition reactions. Rotational barriers in nitrones

Abstract
Rate constants for addition of C-phenyl N-methyl nitrone, the ethylcyclohexyl nitrone (II), and dihydroisoquinoline N-oxide respectively to cyclohexene, norbornene, trans-cyclo-octene, and bicyclo[4,2,0]oct-7-ene have been determined. The barrier (ΔG) to rotation about the formal double bond in the methylene nitrone (II) is estimated to be ca. 23 kcal mol–1. It is concluded that the low reactivity of C-phenyl N-methyl nitrone and analogous ‘class II’ dipoles towards norbornene is due to steric factors.

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