A set of allene‐tethered benzoyloximes (5) has been treated with nBu3SnH. Depending on their substitution pattern, a wide range of compounds has been obtained. If the stannyl radical adds on the allene, the C‐centred radical thus formed undergoes either a 5‐exo ring closure to give the cyclopentene derivatives 7 or a 6‐endo ring closure onto the N atom to give the dihydropyridines 8. If the stannyl radical adds on the benzoyl moiety, an iminyl radical is formed which leads to the 3H‐pyrroles 9 and the alkylidene‐pyrrolines 10. Steric effects as well as polar effects are the factors governing the reaction course.

UIELS-ALDER reactions1 involving vinylallenes have been little studied, especially from the mechanistic point of ~i e w . ~, ~ Accordingly, information on directional effects on such [4 + 21 cycloadditions is particularly pertinent. The interaction of equimolar quantities of vinyla!lene4 and methyl vinyl ketone for 3 hr. at

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