Pyrrolidines from β-Aminoselenides via Radical Cyclization. Diastereoselectivity Control by the N-Substituent

N-Allyl-β-aminoalkyl phenyl selenidesprecursors of 3-aza-5-hexenyl radicalswere prepared by ring opening of N-allylaziridines with benzeneselenol under acidic conditions or by sodium cyanoborohydride reduction of N-allylimines of α-phenylselenenyl ketones. The effect of various N-protective groups (acyl, sulfonyl, or phosphinoyl) on diastereoselectivity in thermally or photochemically initiated 3-aza-5-hexenyl reductive radical cyclization was studied. Whereas N-unprotected derivatives afforded trans-2,4-disubstituded pyrrolidines with good selectivity, the diphenylphosphinoyl group directed cyclization to occur in a highly cis-selective manner.