Synthetic Organic Chemistry Research Laboratory.
J Org Chem. 2010 Nov 19;75(22):7691-703. doi: 10.1021/jo101526b. Epub 2010 Oct 29.
Chemoselective behavior of iodine in different solvents in the electrophilic iodocyclization of o-alkynyl aldehydes is described. o-Alkynyl aldehydes 3a-t on reaction with I2 in CH2Cl2 with appropriate nucleophiles provides pyrano[4,3-b]quinolines 4a-f, via formation of cyclic iodonium intermediate Q; however, using alcohols as a solvent as well as nucleophile, o-alkynyl esters 5a-y were obtained selectively in good to excellent yields via formation of hypoiodide intermediate R. Subsequently, o-alkynyl esters were converted in to pyranoquinolinones 6a-i and isocoumarin 6j by electrophilic iodocyclization. This developed oxidative esterification provides a novel access for the chemoselective synthesis of esters 5q-u from aldehydes 3n-p without oxidizing primary alcohol present in the substrate.
描述了不同溶剂中碘的亲电碘化环化反应中对碘的选择性行为。在适当的亲核试剂存在下，邻炔基醛 3a-t 与 I2 在 CH2Cl2 中反应，通过形成环状碘鎓中间体 Q，生成吡喃并[4,3-b]喹啉 4a-f；然而，使用醇作为溶剂和亲核试剂时，通过形成次碘化物中间体 R，选择性地以良好到优异的收率得到邻炔基酯 5a-y。随后，邻炔基酯通过亲电碘化环化转化为吡喃并喹啉酮 6a-i 和异香豆素 6j。这种开发的氧化酯化反应为从醛 3n-p 中选择性合成酯 5q-u 提供了一种新途径，而无需氧化底物中存在的伯醇。
