Synthesis and stereochemical assignment of heterocycles derived from (2S*,2'S*,4R*,4'R*,6S*,6'S*)-4,4',6,6'-tetramethylperhydro-2,2'-bipyrimidine
作者:Donald C. Craig、Michael Kassiou、Roger W. Read
DOI:10.1021/jo00040a033
日期:1992.7
(2S*,2'S*,4R*,4'R*,6S*,6'S*)-4,4',6,6'-Tetramethylperhydro-2,2'-bipyrimidine (1) reacts with excess formaldehyde in MeOH to give predominantly the tetracycle (1R*,3S*,5R*,7S*,8bS*,8cS*)-1,3,5,7-tetramethylperhydro-3a,4a,7a,8a-tetraazacyclopentano[def]fluorene (2) and in Et2O to give exclusively tetracycle (1R*,3S*,5S*,7R*,8bS*,8cS*)-1,3,5,7-tetramethylperhydro-3a,4a,7a,8a-tetraazacyclopentano[def]fluorene (3). With less formaldehyde, compound 1 yields an unusual 1:5 mixture of trans and cis tricycles, (1R*,3S*,4aS*,4bS*,6S*,8R*)-1,3,6,8-tetramethylperhydro-4,5,8a,9a-tetraazafluorene (5) and (1R*,3S*,4aS*,4bS*,6R*,8S*)-1,3,6,8-tetramethylperhydro-4,5,8a,9a-tetraazafluorene (6), respectively, in MeOH solvent but gives almost exclusively the trans tricycle 5 in Et2O. The structure of tetracycle 2 is supported by X-ray crystallographic data. Compounds 3 and 6 represent new structural types, and they appear to be conformationally stable. A mechanistic scheme for the formation of the tricycles and tetracycles which is consistent with the observed stereochemical changes is proposed.
(2S*,2'S*,4R*,4'R*,6S*,6'S*)-4,4',6,6'-四甲基全氢-2,2'-联嘧啶(1)与过量的甲醛在甲醇中反应,主要生成四环化合物(1R*,3S*,5R*,7S*,8bS*,8cS*)-1,3,5,7-四甲基全氢-3a,4a,7a,8a-四氮杂环戊烷[def]芴(2),而在乙醚中则专一性地生成四环化合物(1R*,3S*,5S*,7R*,8bS*,8cS*)-1,3,5,7-四甲基全氢-3a,4a,7a,8a-四氮杂环戊烷[def]芴(3)。当甲醛用量较小时,化合物1在甲醇溶剂中生成一种罕见的1:5反式与顺式三环化合物混合物,分别为(1R*,3S*,4aS*,4bS*,6S*,8R*)-1,3,6,8-四甲基全氢-4,5,8a,9a-四氮杂芴(5)和(1R*,3S*,4aS*,4bS*,6R*,8S*)-1,3,6,8-四甲基全氢-4,5,8a,9a-四氮杂芴(6),而在乙醚中几乎专一性地生成反式三环化合物5。四环化合物2的结构通过X射线晶体衍射数据得到支持。化合物3和6代表了新的结构类型,且似乎具有构象稳定性。本文提出了一种与观察到的立体化学变化一致的三环和四环形成机制方案。