New Shelf-Stable Halo- and Alkoxy-SubstitutedPyridylboronic Acids and their Suzuki Cross-Coupling Reactions toYield Heteroarylpyridines
作者:Martin R. Bryce、Paul R. Parry、Brian Tarbit
DOI:10.1055/s-2003-39158
日期:——
New shelf-stable pyridylboronic acids have been synthesized: bromine-lithium exchange followed by reaction with triisopropylborate (TIPB) yielded 2-fluoro-5-pyridylboronic acid (4), 3-bromo-5-pyridylboronic acid (5) and 2-ethoxy-5-pyridylboronic acid (6); directed lithiation followed by reaction with trimethylborate (TMB) or TIPB afforded 2-methoxy-3-pyridylboronic acid (8), 3-bromo-6-methoxy-4-pyridylboronic acid (11) and 3-bromo-6-ethoxy-4-pyridylboronic acid (12). Cross-coupling of pyridylboronic acids 4, 6, 8, and 11 with 3-bromoquinoline [Cs2CO3, Pd(PPh3)2Cl2, 1,4-dioxane, 95 °C] gave pyridinylquinoline derivatives 13, 15-17 in 50-77% yields: the analogous reaction of 5 was low yielding due to further in situ reactions of the product 14. Cross-coupling of 12 with 2-bromo-5-nitrothiophene gave 3-bromo-4-(5-nitro-2-thienyl)-6-ethoxypyridine (18).
新合成的稳定的吡啶硼酸具有以下特点:溴锂交换反应随后与三异丙基硼酸酯(TIPB)反应,生成了2-氟-5-吡啶硼酸(4)、3-溴-5-吡啶硼酸(5)和2-乙氧基-5-吡啶硼酸(6);导向锂化反应后与三甲基硼酸酯(TMB)或TIPB反应,得到了2-甲氧基-3-吡啶硼酸(8)、3-溴-6-甲氧基-4-吡啶硼酸(11)和3-溴-6-乙氧基-4-吡啶硼酸(12)。将吡啶硼酸4、6、8和11与3-溴喹啉进行交叉偶联反应([Cs2CO3, Pd(PPh3)2Cl2, 1,4-二氧烷, 95 °C]),得到吡啶基喹啉衍生物13和15-17,产率为50-77%;5的类似反应由于产物14的进一步原位反应,产率较低。将12与2-溴-5-硝基噻吩进行交叉偶联,得到3-溴-4-(5-硝基-2-噻吩基)-6-乙氧基吡啶(18)。