Synthesis of Angularly Fused Pyrrolo[3,2-c]quinoline Lactones and 4-Carboxy-3-vinyl-1,2-dihydroquinolin-2-ones from Morita-Baylis-Hillman Adducts with Labile Acrylate Esters as Michael Acceptors by [3+2] Cycloaddition and Hoffmann-Type Elimination

A number of highly functionalized Morita-BaylisHillman (MBH) adducts have been synthesized from N-methylisatin and aryl and heteroaryl aldehydes as electrophiles and the less well-known propargyl, allyl, and tert-butyl acrylates as labile, activated alkenes in excellent yields. The MBH adducts thus obtained underwent azomethine ylide [3+2] cycloaddition reactions to yield unusual ring-enlarged, angularly fused pyrr-olo[3,2-c] quinoline lactones in excellent yields. Subsequent reaction of the quinolin-2-one lactones under Hoffman elimination conditions (BnBr/KOH) afforded a lactone ring-opened 4-carboxy-3-vinyl-1,2-dihydroquinolin-2-one. A plausible mechanism and discussion of the stereochemical aspects of the cycloaddition reaction are provided.