Regioselective 6-Endo Cyclization of 5-Carbomethoxy-5-hexenyl Radicals: A Convenient Synthesis of Derivatives of the 1-Azabicyclo[2.2.1]heptyl System

摘要: Ring closure of the 5-carbomethoxy-5-hexenyl radical is governed largely by polar effect, and as predicted frontier molecular orbital considerations, endo cyclization predominates, leading to cyclohexyl rather than cyclopentyl-based products. In corresponding β-ammonio species 18, stereoelectronic effects do not distinquish between attack center at C3 or C4, each which represents a 5-exo ring closure. The 18 found cyclize with great rapidity high stereoselectivity give bicyclo[2.2.1]heptane products in accordance expectation based on effects; this transformation an excellent entry physiologically important bicyclic ester 17.