Synthetic applications of N–N linked heterocycles. Part 16. Reactions between carbanions derived from carbon acids with pK<sub>a</sub>7–14 and N-(2,6-dimethyl-4-oxopyridin-1-yl)pyridinium tetrafluoroborate: synthesis of 4-substituted pyridines, and observation of pyridine ringopening reactions
作者:Michael P. Sammes、Christopher W. F. Leung、Alan R. Katritzky
DOI:10.1039/p19810002835
日期:——
Carbanions, derived from carbon acids (5) lying in the pKa range 7–14, add regiospecifically to the pyridinium γ-position in N-(2,6-dimethyl-4-oxopyridin-1-yl)pyridinium tetrafluoroborate (4) to yield 1,4-dihydro-adducts (6). While some intermediates could be fragmented successfully to give 4-substituted pyridines (7), others reverted under similar conditions to the carbon acids (5), due apparently
负碳离子,从碳酸(5)位于在p衍生ķ一个范围7-14,区域专一性添加到吡啶鎓γ位上在Ñ-(2,6-二甲基-4-氧代吡啶-1-基)吡啶鎓四氟硼酸酯(4),得到1,4-二氢加合物(6)。尽管某些中间体可以成功裂解,得到4-取代的吡啶(7),但显然由于存在痕量水,其他中间体在相似条件下还原为碳酸(5)。然而,衍生自丙二腈和氰基乙酸乙酯的阴离子会由于在吡啶鎓α位上的侵蚀而产生开环产物(9),而氰基酯在–30°C时主要产生1,4-加合物,这种情况会恢复在室温下加入到开环化合物中。提供了此异常行为的解释。