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

Abstract

A number of highly functionalized Morita–Baylis–Hillman (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 pyrrolo[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.