A novel tandem Pd-catalyzed intramolecular allylic decarboxylative coupling and “diradical conjugated 1,3-dien-5-yne cycloaromatization”: An unusual ortho -selectivity in the cycloaromatization and the mechanistic implications
作者:Satyanarayana Tummanapalli、Dhanunjaya Naidu Vangapandu、Parthasarathy Muthuraman、Sanjeeva Kambampati、Gnanakalai Shanmugavel
DOI:10.1016/j.tetlet.2017.06.079
日期:2017.8
hindered cyclization products (12–23) via the unusual ortho-selective cycloaromatization; while the meta-alkoxy (1i–m, 1r–t) group provided predominantly the ortho-selective 1,3-dien-5-yne cycloaromatization products, meta-Me group (1 n–q), products formed both via ortho-selective cyclization and para-selective cyclization products in comparable ratio. A novel mechanism involving diradical species
在催化Pd(PPh 3)4和DBU的存在下,Baylis-Hillman醇的丙酸芳基酯的多米诺骨化烯丙基重排,分子内脱羧偶联,炔丙基-丙二烯重排和双自由基1,3-二烯-5-炔环芳构化已经描述了4-苄基萘甲酸的形成。有趣的是,间位取代的丙酸酯(1i – t)通过不寻常的邻位选择性环芳烃化作用提供了空间位阻的环化产物(12 – 23)。而间烷氧基(1i – m,1r –t)组主要提供邻位选择性1,3-二烯基-5yne环芳烃化产品,meta -Me组(1 n – q),是通过邻位选择性环化和对位选择性环化产物以可比的比例形成的产物。已经提出了一种涉及双自由基物种的新机制来解释1,3-二烯-5-炔环芳构化中不寻常的邻位选择性。空间上受阻的邻位选择性环化的优先选择可能归因于具有更稳定的邻位甲氧基环己二烯基团部分(驱动力)的过渡态自由基的形成。