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).
Multimetallic Iridium-Tin (Ir-Sn<sub>3</sub>) Catalyst in<i>N</i>-Acyliminium Ion Chemistry: Synthesis of 3-Substituted Isoindolinones<i>via</i>Intra- and Intermolecular Amidoalkylation Reaction
作者:Arnab Kumar Maity、Sujit Roy
DOI:10.1002/adsc.201400234
日期:2014.8.11
AbstractThe multimetallic iridium‐tritin (Ir‐Sn3) complex [Cp*Ir(SnCl3)2SnCl2(H2O)2}] (1) proved to be a highly effective catalyst towards COH bond activation of γ‐hydroxylactams, leading to a nucleophilic substitution reaction known as the α‐amidoalkylation reaction. Catalyst 1 can be easily synthesized from the reaction of (pentamethylcyclocyclopentadienyl)iridium dichloride dimer [Cp*IrCl2]2} and tin(II) dichloride (SnCl2). In terms of catalyst loading, reaction conditions and yields of the product formed, 1 is found to be superior compared to classical Lewis acid catalysts. Different carbon (arenes, heteroarenes, allyltrimethylsilane, 1,3‐dicarbonyls) and heteroatom (alcohols, thiols, amides and sulfonamides) nucleophiles have been successfully employed in the intramolecular and intermolecular alkylations, as well as in heterocyclization reactions. In the majority of cases good to excellent yields of 3‐substituted isoindolinones and 5‐substituted pyrrolidin‐2‐ones have been obtained. Besides, the reactions are also atom economical and salt free. It is proposed that the multimetallic Ir‐Sn3 catalyst behaves as a mild and selective Lewis acid to activate the γ‐hydroxylactam towards the formation of the N‐acyliminium ion; the latter being trapped by potent nucleophiles leading to the desired products.magnified image
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