172978-85-7Relevant articles and documents
Annulation Based on 6-Endo-Trig Radical Cyclization: Regioselectivity and Diastereoselectivity
Ward, Dale E.,Gai, Yuanzhu,Kaller, Brian F.
, p. 7830 - 7836 (1995)
The development of a annulation strategy based on sequential "two-electron" and "one-electron" allylation of β-substituted aldehydes and derivatives with the bifunctional isobutene conjunctive reagent 1 is described.The key step involves an unusual 6-endo-trig radical cyclization.Yields of 6-endo products are improved if the PhS group is oxidized to a PhSO2 group prior to cyclization.The structural factors affecting the regioselectivity and stereoselectivity of the cyclization are examined.In general, the stereoselectivity of 6-endo-trig cyclization of 5-hexenyl radicals can be rationalized by conformational analysis of chairlike transition states and can be calculated effectively with an MM2 force field model.High 6-endo regioselectivity requires a strong driving force.Fragmentable allylic groups (R3Sn, PhSO2, and to a lesser extent PhS) are shown to be sufficiently activating to achieve 6-endo regioselectivity.
