2.17 Addition to N-Acyliminium Ions of Heteroatoms such as Oxygen, Nitrogen, Sulfur, and Selenium as Internal Nucleophiles

Bi(OTf)3‐Catalysed Access to 2,3‐Substituted Isoindolinones and Tricyclic N,O‐Acetals by Trapping of Bis‐N‐Acyliminium Species in a Tandem Process

“…All characteristic data of cyclised compound 15a are identical to those published recently by Roy and co‐workers during their application of a bimetallic Ir–Sn catalyst for tandem reaction sequence of heterocyclisation/isomerisation/π‐cyclisation using 3‐hydroxy‐ N ‐phenyoxymethylisoindolin‐1‐one . This sequence was initially proposed by us in reports dealing with sulfur, oxygen, and selenium‐containing N ‐acyliminum precursors. o ‐Substituted phenols with Bn, OH and Br also undergo the desired chemistry to render cyclic N,O‐acetals 15b – d in moderate to low yields of 43 %, 45 % and 27 %, respectively.…”

“…Although C–C bond forming methods have been extensively investigated, approaches to the formation of C–heteroatom bonds remain scarce. Yet C–heteroatom bond formation constitutes a novel and powerful strategy by which to access new complex compounds containing cyclic mixed N,O‐, N,N‐, N,S‐, and N,Se‐acetals, as we have recently noted . Interestingly, the application of these cations as 1,3‐bis‐electrophile units has been reported in only two reaction series with external carbon and oxygen nucleophiles (Figure ) leading to piperidines, 2‐oxo‐ N ‐arylpyrrolidine‐1‐carboxamides and 1,3‐diaryl ureas, respectively.…”

Triflic Acid Catalyzed Intermolecular α-Amination of Pterolactams To Give 5-Arylaminopyrrolidinones via N-Acyliminium Species

“…19 Interestingly, the intramolecular version of the C-N bond-forming reaction based on the reactivity of an N-acyliminium ion 20 or vinylogue 21 seems to give good results, as reported by many groups and compiled by us recently. 22 In connection with our interest in the heterocyclization process involving N-acyliminium chemistry, 20, 22 we report herein our investigations on the reaction of 5-methoxypyrrolidones (pterolactams) with anilines or their corresponding N-anilino-trimethylsilanes under acid-catalyzed conditions. The main objective here was to gain insight into the aza-amidoalkylation process in which the origin of the nitrogen fragment being incorporated into the α-position of the lactam system may play a pivotal role in the effectiveness of the pathway.…”

γ-Hydroxy-γ-butyrolactams as 1,2-bis-electrophiles in a Brønsted/Lewis acid-free synthesis of condensed nitrogen heterocycles

“…In a search for alternatives, we paid attention to 3,5diaryl-5-hydroxypyrrolin-2-ones -fairly stable reagents. These compounds are relatively stable reagents that, upon exposure to acidic or thermal conditions, can undergo dehydration to generate highly reactive N-acyliminium ions (Scheme 2a) 18,19 able to catch a wide range of both carbon 20 and heteroatom 21 nucleophiles and therefore provide a versatile and controllable method of carbon-carbon and carbon-heteroatom bond formation (Scheme 2b and c). [22][23][24][25][26] While the literature thoroughly describes hemiaminal fragment transformations, only a single instance of subsequent Michael addition at the acrylamide double bond has been reported (Scheme 2d).…”