π-Aromatic and Sulfur Nucleophilic Partners in Cationic π-Cyclizations: Intramolecular Amidoalkylation and Thioamidoalkylation Cyclization via ω-Carbinol Lactams<sup>1</sup><sup>,</sup><sup>2</sup>
作者:Nicolas Hucher、Bernard Decroix、Adam Daïch
DOI:10.1021/jo0156316
日期:2001.6.1
described. During this reaction, we have shown that omega-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 omega-carbinol lactams 14b-e substituted at C-angular position afforded the corresponding isoindolobenzothiazinones
Access to the New Isoindolo[1,3]benzothiazocinones via the Combination of N-Acyliminium Chemistry and Friedel-Crafts Type π-Cyclization
作者:Adam Daïch、Armelle Cul、Bernard Decroix、Gérard Sanz、Luc Van Hijfte
DOI:10.3987/com-04-s(p)18
日期:——
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
Bismuth(III) triflate was found to promote the formation of stable cyclic N-acyliminium species in remarkable catalytic amounts (1 mol %). The alpha-amidoalkylation process seems to be effective in intermolecular and intramolecular manners leading to alpha-substituted lactams and heterocyclic systems containing azacycles, respectively. By comparing our results with those obtained with the classical Lewis acids as catalysts, it was evidenced clearly that the use of bismuth(III) triflate had been efficient for nearly all alpha-acetoxy lactams we used, except for N-acyliminium precursors bearing a sulfur atom. Also, the process seems to be easy, general, and clean, having diastereoselectivity comparable to protocols using classical Lewis acids and resulting in the formation of polyheterocyclic systems in good to excellent yields (64-99% in acetonitrile as solvent).