Exocyclic–Endocyclic N-Acyliminium Ion Equilibration via an Intramolecular α-Thioamidoalkylation in the Synthesis of Fused N,S-Heterocyclic Systems: Some New Parameters
✍ Scribed by Nicolas Hucher; Anthony Pesquet; Pierre Netchitaïlo; Adam Daïch
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 231 KB
- Volume
- 2005
- Category
- Article
- ISSN
- 1434-193X
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
The reactivity of N‐[aryl(or alkyl)thio(oxo or seleno)alkylamidals 6 bearing the N‐(CH~2~)~n~‐X‐(CH~2~)~m~‐Ar functionality towards neat TFA has been examined. Substrates of type 6 give, together with the products 11, 17, 19, and 25 of the “expected” π‐cyclization process, the “unexpected” products 12, 18, and 26 resulting from a new tandem heteroamidoalkylation/isomerization/π‐cyclization. The composition of the final isomeric mixture depends on the temperature of the reaction, with a high selectivity in favor of the “expected” π‐cyclization product 11 as a thermodynamic isomer. Furthermore, the results demonstrate again the relevance of TFA catalysis and support two reaction pathways involving the formation of an aza‐sulfonium cation A as a valuable intermediate which undergoes the π‐cyclization process alone or in tandem with the thiocyclization/isomerization to give the cyclized products cited above. For the latter tandem reaction, we have established clearly that the n value should be equal to 1, the process can be performed independently for both the succinimide and phthalimide series, the reaction depends on the nucleophilicity of the heteroatom, and can be generalized to other heterocycles. Only the role of the benzene substitution has still to be totally elucidated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)