Dithionite adducts of pyridinium salts: regioselectivity of formation and mechanisms of decomposition
作者:Vincenzo Carelli、Felice Liberatore、Luigi Scipione、Barbara Di Rienzo、Silvano Tortorella
DOI:10.1016/j.tet.2005.07.096
日期:2005.10
characterize the adducts formed, in alkaline solutions, by the attack of dithionite anion on 3-carbamoyl or 3-cyano substituted pyridinium salts. In all studied cases, only 1,4-dihydropyridine-4-sulfinates, formed by attack of dithionite oxyanion on the carbon 4 of pyridinium ring, were found. This absolute regioselectivity seems to suggest a very specific interaction between the pyridinium cation and the
1 H和13 C NMR光谱已用于检测和表征碱性溶液中连二亚硫酸根阴离子对3-氨基甲酰基或3-氰基取代的吡啶鎓盐的攻击而形成的加合物。在所有研究的情况下,仅发现由连二亚硫酸根氧阴离子攻击吡啶鎓环的碳4形成的1,4-二氢吡啶-4-亚磺酸盐。这种绝对的区域选择性似乎表明吡啶鎓阳离子与连二亚硫酸盐之间通过形成刚性取向的离子对形成了非常特殊的相互作用,从而决定了进攻的位置。在弱碱性溶液中,加合物根据两种机理S N i和S N i'分解:S Ni路径在所有研究的情况下均有效,并保留了1,4-二氢结构,产生相应的1,4-二氢吡啶,而S N i'路径涉及2,3或5,6双键的移位,从而产生1,2 -或1,6-二氢吡啶。除了1,4-二氢异构体之外,1,2-或1,6-二氢吡啶的形成还取决于它们各自的热力学稳定性。