Mild acylation of fischer indole with 5-aryl-2,3-dihydrofuran-2,3-diones

Acylation of the enamino tautomer of 2-azaspiro[4.5]deca-1,6,9-trien-8-ones with 5-arylfuran-2,3-diones. Crystal and molecular structure of (2Z,5Z)-3-Hydroxy-5-(6,9-dimethoxy-3,3-dimethyl-8-oxo-2-azaspiro[4.5]deca-6,9-dien-1-ylidene)-1-phenylpent-2-ene-1,4-dione

“…The mechanism of formation of compounds III is likely to involve acylation of the =CH 2 group in enamino tautomer A of spiro compound II by the C 2 =O carbonyl group of 5-arylfuran-2,3-dione I, followed by cleavage of the furan ring at the O 1 -C 2 bond, as described previously for the reactions of 5-arylfuran-2,3-diones with such heterocyclic enamines as 1-methyl-3,4-dihydroisoquinolines [5] and Fischer base [6]. Considerable steric hindrances created by geminal methyl groups in the pyrrolidine fragment and spiro-fused naphthalene ring in molecule IIa, as well as by additional substituents in positions 3 and 6 of molecules IIb and IIc, do not prevent them from reacting with 5-arylfuran-2,3-diones.…”

“…On the other hand, furandiones themselves can react with nucleophiles to produce aroylpyruvoyl derivatives at a temperature below that required for generation of aroylketenes [1,4]. We previously showed that some heterocyclic enamines of the 1-methyl-3,4-dihydroisoquinoline, 1-methyl-2-azaspiro [4.5]deca-1,6,9-trien-8-one, and 2-methylidene-1,3,3-trimethyl-2,3-dihydro-1H-indole (Fisher's base) series can be acylated with 5-arylfuran-2,3-diones to give the corresponding aroylpyruvoyl derivatives [5][6][7]. In continuation of our studies on the reactions of 5-arylfuran-2,3-diones with spirans of the 2-azaspiro- [4.5]deca-1,6,9-trien-8-one series in the present work we examined how additional substituents in positions 3 and 6 of the latter affect the direction of their reaction with the former.…”