Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.
J Org Chem. 2010 Sep 3;75(17):5953-62. doi: 10.1021/jo101238x.
Introduction of a nitrogen atom at one of the acetylenic termini of 10-, 11-, 12-, and 13-membered benzannulated cyclic enediynes results in a complete suppression of the conventional radical Bergman reaction in favor of a polar cycloaromatization. The latter reaction is catalyzed by acids and proceeds via initial protonation of an ynamide fragment. The resulting ketenimmonium cation then cyclizes to produce naphthyl cation, which rapidly reacts with nucleophiles or undergoes Friedel-Crafts addition to aromatic compounds. In alcohols, addition of the nucleophilic solvent across the activated triple bond competes with the cyclization reaction. The ratio of cyclized to solvolysis products decreases with the increase in ring size.
在 10-、11-、12-和 13-员环并环二烯炔的一个炔键末端引入一个氮原子，会完全抑制常规的自由基 Bergman 反应，有利于极性环芳构化。后一种反应由酸催化，通过对炔酰胺片段的初始质子化进行。生成的烯酮亚铵阳离子然后环化生成萘基阳离子，该阳离子迅速与亲核试剂反应或与芳族化合物发生傅-克加成反应。在醇中，亲核溶剂通过活化的三键加成与环化反应竞争。环化产物与溶剂解产物的比例随环尺寸的增加而降低。
