Phenylsulfonyl Ene−Allenes as Efficient Precursors to Bicyclic Systems via Intramolecular [2 + 2]-Cycloaddition Reactions
作者:Albert Padwa、Helmut Lipka、Scott H. Watterson、S. Shaun Murphree
DOI:10.1021/jo0345796
日期:2003.8.1
stereospecificity involves initial diradical formation, followed by a rapid ring closure to the more stable cis-fused ring system. The tether may be equipped with heteroatoms, allowing for the formation of fused heterocycles (e.g., 61), and the cycloaddition can be facilitated by the introduction of sterically bulky groups and/or by conformational rigidity to the tether. Other modes of cyclization were observed
制备了具有双键的双苯基磺酰基丙二烯丙二烯衍生物,该双键被束缚在丙二烯的α-位或γ-位。这些底物在未活化的异丙苯双键上进行了高度区域和立体定向的热[2 + 2]-环加成反应,在α系链的丙二烯和近端加合物(即25)的情况下,形成了远端的环加合物(即57)。的情况下,γ系链的烯。所观察到的立体特异性的机理原理包括最初的双自由基形成,随后是快速的环闭合至更稳定的顺式稠合的环系统。系链可以装备有杂原子,从而允许稠合的杂环的形成(例如61),并且可以通过引入空间上庞大的基团和/或通过对系链的构象刚性来促进环加成。在苯亚磺酸钠或路易斯酸的存在下观察到其他环化方式,在这种情况下,极性机理占优势。对于[4 + 2]-环加成,其化学选择性相反,后者更喜欢与乙烯基砜部分接合,而与系链是连接到丙二烯的α-位还是gamma位无关。