Regioselective Inverse Electron Demand Diels−Alder Reactions of <i>N</i>-Acyl 6-Amino-3-(methylthio)-1,2,4,5-tetrazines
作者:Dale L. Boger、Robert P. Schaum、Robert M. Garbaccio
DOI:10.1021/jo980795g
日期:1998.9.1
order of reactivity with electron-rich dienophiles was observed with both 2 and 3 being more reactive than 3,6-bis(methylthio)-1,2,4,5-tetrazine (1, i.e. 3 > 2 > 1), and both 3 and 4 were shown to be more robust than 2 at the higher temperatures necessary for [4 + 2] cycloaddition with less reactive dienophiles. The cycloaddition regioselectivity is consistent with the polarization of the diene and the
6-[(叔丁氧羰基)氨基] -3-(甲硫基)-1,2,4,5-四嗪(2),6-(乙酰氨基)-3-(甲硫基)的区域选择性逆电子需求Diels-Alder反应公开了)-1,2,4,5-四嗪(3)和6-(苄氧基羰基)氨基-3-(甲硫基)-1,2,4,5-四嗪(4)。这三者均与富含电子的亲二烯体进行区域选择性[4 + 2]环加成反应,从而以优异的收率形成了相应的功能化1,2-二嗪。观察到与富电子的亲二烯体的反应顺序,其中2和3均比3,6-双(甲硫基)-1,2,4,5-四嗪(1,即3> 2> 1)更具反应性,并且在[4 + 2]环加成反应所需的较高温度下,反应性较少的亲二烯体,3和4都比2更坚固。环加成区域选择性与二烯的极化和甲硫基在C-3处稳定部分负电荷的能力以及N-酰基氨基在C-6处稳定部分正电荷的能力是一致的。尽管未活化炔烃的分子间反应没有进行或需要高温和较长的反应时间,但利用链状未活化乙炔的