Regioselective Synthesis of Isochromenones by Iron(III)/PhSeSePh-Mediated Cyclization of 2-Alkynylaryl Esters

A series of 4-Se-(Te, S)-isochromenones and 3-substituted isochromenones were synthesized in good yields via FeCl3-mediated cyclization of alkynylaryl esters with different diorganyl dichalcogenides. This methodology was carried out at room temperature, using inexpensive and environmentally friendly iron salts as metallic source and under air atmosphere. The reaction showed to be tolerant to a range of substituents bonded into the aromatic ring of the diorganyl dichalcogenides as well as to alkyl groups directly bonded to the chalcogen atom. Alternatively, the cyclization reaction of 2-alkynylaryl esters with FeCl3, in the absence of diorganyl dichalcogenide, gave the isochromenones without the chalcogen moiety in the structure. This approach proved to be highly regioselective, providing only six-membered ring products, once the possible five-membered products were not observed in any experiments.

本研究通过三氯化铁（FeCl3）介导的炔芳基酯（alkynylaryl esters）与不同二有机二硫族化合物（diorganyl dichalcogenides）的环化反应，以良好收率合成了一系列4-硒代（碲代、硫代）异色满酮（4-Se-(Te, S)-isochromenones）及3-取代异色满酮（3-substituted isochromenones）。该方法于室温下进行，以廉价且环境友好的铁盐作为金属源，且可在空气氛围中完成。反应对二有机二硫族化合物芳环上的各类取代基以及直接与硫族原子相连的烷基均具有良好的耐受性。另一方面，在无二有机二硫族化合物存在时，2-炔基芳基酯（2-alkynylaryl esters）与三氯化铁发生环化反应，可得到结构中不含硫族基团（chalcogen moiety）的异色满酮。该方法展现出极高的区域选择性，仅生成六元环产物，所有实验中均未观测到可能的五元环产物。