Pyrrolidinone rings formation

A three-component one-pot coupling of 2,6-dimethylphenyl isocyanide, methyl 2,4-dioxopentanoate and alkynoic esters leads to the isatin-like compounds (or fused pyrans) 20 (Scheme 5). The reaction proceeds by initial formation of the zwitterionic intermediate 21, which is protonated by methyl 2,4-dioxopentanoate. Attack of the newly generated nucleophile then forms the intermediate 22. The pyrrolidinone ring is formed upon loss of methanol and electrocyclization then occurs to afford the desired 2//-pyrans (Scheme 5) <2005S1049>. 

Formation of Pyrrole, Pyrrolidine, and Pyrrolidinone Rings 168 7. Concluding Remarks 181... 

Radical cyclization is compatible with the presence of other functional groups. Treatment of XCH2CON(R)-C(R )=CH2 derivatives (X = Cl, Br, 1) with Ph3SnH and AIBN led to formation of a lactam via radical cyclization. " Cyclization of N-iodoethyl-5-vinyl-2-pyrrolidinone led to the corresponding bicyclic lactam, " and there are other examples of radical cyclization with molecules containing a lactam unit " or an amide unit. Radical cyclization occurs with enamines as well. Photochemical irradiation of A,A-dialIyl acrylamide leads to formation of a lactam ring, and in this case thiophenol was added to generate the phenylthio derivative. Phenylseleno N-allylamines lead to cyclic amines. co-Iodo acrylate esters cyclize to form lactones. " ... 

Reaction of the 2-amino-substituted thiophene 244 with pyrrolidinone in the presence of phosphorus oxychloride led to efficient formation of the central six-membered ring of tricycle 245 in 57% yield (Equation 67)... 

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