6-Endo- and 5-exo-digonal cyclizations of o-hydroxyphenyl ethynyl ketones: A key step for highly selective benzopyranone formation
作者:Kazuhiko Nakatani、Akimitsu Okamoto、Isao Saito
DOI:10.1016/0040-4020(96)00480-2
日期:1996.7
critical for the products formation. We generated phenoxide ion under aprotic conditions in situ by desilylation of o-silyloxyphenyl ethynyl ketones with spray dried potassium fluoride and 18-crown-6 in anhydrous DMF. Under these conditions the cyclization of variety o-hydroxyphenyl ethynyl ketones proceeded smoothly to produce benzopyranone derivatives with exceedingly high selectivity. Theoretical and experimental
从理论和实验的角度对邻羟基苯乙炔基酮的环化进行了研究,以便开发出有效的合成方法来构建具有重要生物活性的2-取代的吡喃酮。从头算研究在环化的HF / 6–31G *水平下表明,分别在非质子传递介质中产生苯并吡喃酮和苯并呋喃酮的6-内-己二酮和5 -exo-digonal环化都是吸热的和可逆的,并且其不可逆的质子化产生的阴离子对于产物形成至关重要。我们产生了质子惰性的条件下,苯酚离子原位通过脱甲硅基的ø-甲硅烷基氧苯基乙炔基酮,在无水DMF中喷雾干燥的氟化钾和18-crown-6。在这些条件下,各种邻羟基苯乙炔基酮的环化反应顺利进行,以产生具有极高选择性的苯并吡喃酮衍生物。理论和实验结果强烈表明,影响生成的苯并吡喃酮阴离子的质子化的少量质子供体对于高6-内-对-对-丁二烯选择性是必不可少的。