Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany.
Org Biomol Chem. 2012 Dec 21;10(47):9464-73. doi: 10.1039/c2ob26689j. Epub 2012 Nov 5.
Benzofuroquinolines were prepared by a new type of Pd catalyzed annulation reaction. In the first step, 2-alkynyl-3-bromobenzofurans were prepared by Sonogashira reactions of 2,3-dibromobenzofuran. Their Pd catalyzed reaction with electron-rich anilines afforded benzofuroquinolines by a domino C-N coupling/annulation process. This reaction proceeds as a C,N-cyclization via the nitrogen atom and the ortho-carbon of the aniline. Similarly, furoquinolines were prepared from 2,3-dibromofuran. In contrast, benzofuropyrroles and furopyrroles were formed by N,N-cyclization when electron-poor anilines were used. Earlier, we reported results related to the thiophene and benzothiophene series. Quinolines were formed from 2,3-dibromobenzothiophene when electron rich anilines were used. In contrast, pyrroles were obtained in the case of electron-poor anilines. On the other hand, pyrroles were generally obtained, not depending on the type of aniline, when 2,3-dibromothiophene was employed as the starting material. In the present article, a detailed DFT study related to the mechanism (quinoline versus pyrrole formation) is reported which provides a rationalization of the selectivities observed for the furan, benzofuran, thiophene and benzothiophene series and for the different selectivities observed for electron-rich and -poor anilines.
苯并呋喃并喹啉类化合物是通过一种新型的 Pd 催化的环化反应制备的。在第一步中，通过 Sonogashira 反应，用 2,3-二溴苯并呋喃制备 2-炔基-3-溴苯并呋喃。它们与富电子苯胺的 Pd 催化反应通过 C-N 偶联/环化过程得到苯并呋喃并喹啉类化合物。该反应通过苯胺的氮原子和邻位碳原子进行 C,N-环化。同样，用 2,3-二溴呋喃也可以制备呋喃并喹啉。相比之下，当使用缺电子苯胺时，通过 N,N-环化形成苯并呋喃并吡咯和呋喃并吡咯。早期，我们报道了噻吩和苯并噻吩系列的相关结果。当使用富电子苯胺时，从 2,3-二溴苯并噻吩形成喹啉。相反，当使用缺电子苯胺时，得到吡咯。另一方面，当使用 2,3-二溴噻吩作为起始原料时，通常会得到吡咯，而与苯胺的类型无关。在本文中，报道了与机制（喹啉与吡咯形成）相关的详细 DFT 研究，为呋喃、苯并呋喃、噻吩和苯并噻吩系列以及富电子和缺电子苯胺观察到的不同选择性提供了合理化解释。
