Bond Rotation Dynamics of Enamides: The Effect of the Acyl Group and Potential for Chirality Transfer during 5-Endo Trig Radical Cyclizations

作者：Clark Andrew J^*; Curran Dennis P; Geden Joanna V; James Natalie; Wilson Paul

来源：Journal of Organic Chemistry, 2011, 76(11): 4546-4551.

DOI：10.1021/jo200343z

Barriers to rotation of the N-alkenyl bond in a series of N-cycloalkenyl-N-benzyl acetamide derivatives have been measured in different solvents by variable-temperature NMR experiments. The barriers range from 9.7 to 14.2 kcal/mol, depending on substituents on the acetamide acyl group. Polar solvents such as chloroform and methanol increase the barrier to rotation compared to nonpolar solvents such as toluene. The barrier to rotation of "mimics" for acetamide-based radicals are estimated. The relative order of the values of k(rot) for different acyl groups parallels their reported Taft E(s) paramaters. For successful chirality transfer in 5-endo trig radical cyclization, it is evident that rotations would need to be significantly slower than those reported here.

• 出版日期2011-6-3