Furan ring opening–pyrrole ring closure. A simple route to 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazin-3-ones

Cycloamination strategies for renewable N-heterocycles

“…For instance, a furan ring opening-pyrrole ring closure strategy has been adopted for the synthesis of pyrrole-fused heterocycles such as pyrrolo [1,2-a] [1,4]diazepines and 1,2,3,4tetrahydropyrrolo[1,2-a]pyrazin-3-ones. 289,290 In view of the feasibility of furan-ring opening, biofuranics and their derivatives (e.g., levulinic acid) are extensively used for the construction of complex azaheterocycles like indolo [3,2-c]quinolines and bicyclic heterocycles. 291,292 Direct transformation of biomass sugars to azaheterocycles has been investigated with profound results, 293,294 while most studies of upgrading lignin are more focused on its model molecules such as 2-phenoxy acetophenone and aromatic aldehydes via modified approaches based on conventional reactions.…”

Furan's Gambit: Electrophile‐Attack‐Triggered Sacrifice of Furan Rings for the Intramolecular Construction of Azaheterocycles

“…Catalysis by Brønsted acids allows related reactions to be performed under much milder conditions. Recently we showed that pyrrolo[1,2‐ a ]pyrazine derivatives 54 can be synthesized by the treatment of N ‐furfurylamides of α‐amino acids 53 with HCl/AcOH at room temperature (Scheme ) 25a. This transformation proceeded in reasonable yields (57–74 %) when R 2 = H. Introduction of an alkyl or aryl group into the α position of the furfuryl moiety led to a significant decrease in yield, which was explained by the increased stability of the α‐substituted furfuryl cations.…”

Furan Ring Opening – Pyridine Ring Closure: An Efficient Approach towards 6H‐Isochromeno[4,3‐b]pyridin‐6‐ones from Readily Available Furans and Phthalaldehydic Acid Methyl Esters

“…Meanwhile, the target products of such transformation, namely, N ‐substituted α‐arylfurfurylamines have been solidly established as promising objects for a variety of subsequent structural modifications, which opens up new opportunities in the synthesis of complex natural products and drug molecules. Furfurylamines of this type are well recognized to undergo a number of furan ring transforming processes, such as aza‐Achmatowicz, aza‐Piancatelli rearrangements, intra‐ and intermolecular Diels–Alder reactions, and protolytic furan recyclization reactions that lead to an array of diverse carbo‐ and heterocycles. Moreover, the presence of an ortho ‐substituent in the aryl ring renders the target ortho ‐functionalized N ‐alkoxycarbonyl α‐(α‐furyl)benzylamines appropriate substrates for the Butin reaction, which was shown to provide access to a variety of benzannelated polyheterocyclic compounds.…”