Effect of Temperature on Atom Transfer Cyclization Reactions of Allylic α-Iodo Esters and Amides

Article abstract of DOI:10.1021/jo00008a032

Atom-transfer cyclizations of allyl iodoacetates and N-allyl-N-methyliodoacetamides are much more efficient at 80 deg C than at 25 deg C.At 80 deg C, β-(iodomethyl) lactones and lactams are formed rapidly and in good yield under standard atom-transfer conditions (sunlamp irradiation of iodide and 10percent hexabutylditin in benzene for 10-60 min).It is proposed that this temperature effect is responsible for some unusual observations by Jolly and Livinghouse in the cyclization of N-cyclohexenyl-N-methyliodoacetamide.The results suggest that the beneficial effect of temperature arises because an increase in the rate of rotation of t he OC-O or OC-N bond in the intermediate radicals begins to convert syn radicals (which cannot cyclize) to anti radicals (which can cyclize).Consistent with this hypothesis, the radical derived from N,N-diallyliodoacetamide (which always has a favorable arrangement for cyclization) closes with excellent efficiency at 25 deg C.