Iridium-Catalyzed, Silyl-Directed Borylation of Nitrogen-Containing Heterocycles
摘要:
Selective methods for the functionalization of indoles and other nitrogen heterocycles would provide access to the core structures of many natural products and pharmaceuticals. Although there are many methods and strategies for the synthesis of substituted indoles or functionalization of the azole ring, strategies for the selective functionalization of the benzo-fused portion of the indole skeleton, particularly the 7-position, are less common. We report a one-pot, iridium-catalyzed, silyl-directed C-H borylation of indoles at the 7-position. This process occurs in high yield with a variety of substituted indoles, and conversions of the 7-borylindole products to 7-aryl-, 7-cinnamyl-, and 7-haloindoles are demonstrated. The Ir-catalyzed, silyl-directed C-H borylation also occurs with several other nitrogen heterocycles, including carbazole, phenothiazines, and tetrahydroquinoline. The utility of this methodology is highlighted by the one-pot synthesis of a member of the pyrrolophenanthridone class of alkaloid natural products.
Borylation directed borylation of <i>N</i>-alkyl anilines using iodine activated pyrazaboles
作者:C. R. P. Millet、E. Noone、A. V. Schellbach、J. Pahl、J. Łosiewicz、G. S. Nichol、M. J. Ingleson
DOI:10.1039/d3sc04269c
日期:——
[H(NTf2)B(μ-C3N2H3)]2, is highly effective for ortho-borylation, with this process proceeding through N–H borylation and then ortho C–H borylation. The activation of pyrazabole by I2 was developed as a cheaper and simpler alternative to using HNTf2 as the activator. The addition of I2 forms mono or ditopic pyrazabole electrophiles dependent on stoichiometry. The ditopic electrophile [H(I)B(μ-C3N2H3)]2 was also
双亲电吡唑啉衍生物(吡唑唑= [H 2 B(μ-C 3 N 2 H 3 )] 2)与一当量组合。碱的作用是使N-烷基苯胺发生邻位硼基化。初步研究发现双(三氟甲烷)磺酰亚胺([NTf 2 ] − )吡唑啉衍生物[H(NTf 2 )B(μ-C 3 N 2 H 3 )] 2对于邻位硼基化非常有效,因此过程先进行 N-H 硼化,然后进行邻位C-H 硼化。I 2对吡唑啉的活化被开发为使用 HNTf 2作为活化剂的更便宜且更简单的替代方案。I 2的添加形成取决于化学计量的单位或二位吡唑啉亲电体。双位亲电子试剂 [H(I)B(μ-C 3 N 2 H 3 )] 2对N -烷基苯胺的邻位硼化也有效,初级 C–H 硼化产物很容易转化为频哪醇硼酸酯(BPin)衍生物。使用二-NTf 2 -和二碘-吡唑啉同系物的硼化反应的比较表明,后者需要更多的强迫条件。此外,碘化物的存在会导致副产物的竞争性形成,包括 [HB(μ-C