Exocyclic-EndocyclicN-Acyliminium Ion Equilibration via an Intramolecular α-Thioamidoalkylation in the Synthesis of Fused N,S-Heterocyclic Systems: Some New Parameters
The reactivity of N-[aryl(or alkyl)thio(oxo or seleno)alkylamidals 6 bearing the N-(CH2)n-X-(CH2)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