π-Aromatic and Sulfur Nucleophilic Partners in Cationic π-Cyclizations: Intramolecular Amidoalkylation and Thioamidoalkylation Cyclization via ω-Carbinol Lactams1,2

NaBH4 reduction of imides 1 and 6a,b,c followed by a π-cyclization of the resultant N-acyliminium
ions, generated in trifluoroacetic acid conditions, afforded two positional isomers, isoindolobenzothiazolinones 4 and 8, respectively. These ring closures proceeded via an intramolecular
α-amidoalkylation with the classical π-aromatic or the atypical sulfur atom as an internal
nucleophile. A ready access to the related six-membered N,S-heterocyclic compounds such as
isoindolobenzothiazinones 20a and 21a is also described. During this reaction, we have shown that
ω-carbinol lactam precursor 14a led to endocyclic and exocyclic N-acyliminium ions 18a and 19a
in equilibrium via the cyclic aza-sulfonium ion A. The latter furnished the expected products 20a
and 21a in good yields. Similarly, different ω-carbinol lactams 14b−e substituted at C-angular
position afforded the corresponding isoindolobenzothiazinones 20b−e and 21b−e bearing an angular
alkyl, aralkyl, or aryl group. In the case of methyl 14b and benzyl 14e groups, an additional amount
of the dehydration products 16b and 31 was isolated. These results indicate that the isomerization-π-cyclization takes place via the cleavage of the thioether linkage in acidic medium.

以NaBH4对亚胺1和6a,b,c进行还原反应，随后在 trifluoroacetic acid 条件下，对生成的N-acyliminium离子进行π-环化反应，成功获得了两种位置异构体，即异喹啉苯并噻唑啉酮4和8。该环闭过程通过分子内α-酰胺烷基化反应完成，其中经典π-芳香性或非典型的硫原子作为内源亲核试剂。此外，还描述了如何便捷地合成相关的六元N,S-杂环化合物，如异喹啉苯并噻唑啉酮20a和21a。在本反应过程中，我们观察到ω-羟基酰胺前体14a通过平衡反应生成内环和外环N-acyliminium离子18a和19a，这些离子通过环状亚磺酰离子A进一步提供了预期的产物20a和21a，并取得了良好的产率。类似地，不同C-角位的ω-羟基酰胺14b−e取代物提供了相应的异喹啉苯并噻唑啉酮20b−e和21b−e，并带有角位烷基、芳基或芳基烷基。在甲基14b和苄基14e基团的情况下，还分离出了额外的脱水产物16b和31。这些结果揭示了异构化和π-环化反应是通过在酸性介质中断裂硫醚键来实现的。