Direct heterocyclization of tetrahydroisoquinolin-1-ylideneacetic acids by the action of 5-arylfuran-2,3-diones

We previously described acylation with 5-arylfuran-2,3-diones of the β-CH group in the enamino tautomers of s ubstituted 1-methyl-3,4-dihydroisoquinolines having no other functional groups. These reactions afforded (2Z,5Z)-1-aryl-3-hydroxy-5-[3,3-dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene]pent2-ene-1,4-diones [1, 2]. In the present communication we report on the reaction of 5-arylfuran-2,3-diones with 1-methylidene-1,2,3,4-tetrahydroisoquinolines possessing an additional functional group at the exocyclic carbon atom attached to C 1 . 5-Arylfuran-2,3-diones Ia and Ib reacted with [3,3-dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene]acetamides IIa and IIb at a ratio of 1 : 1 on heating in boiling anhydrous benzene (reaction time 1–2 h). The progress of the reactions was monitored by thin-layer chromatography, and the products were the corresponding (3E,5Z)-5-(2-aryl-2-oxoethylidene)-3-[3,3dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene]pyrrolidine-2,4-diones IIIa and IIIb whose structure was determined by X-ray analysis.