DIELS-ALDER REACTIONS OF PYRIDINE O-QUINODIMETHANE ANALOGUES GENERATED FROM FUNCTIONALISED O-BIS(CHLOROMETHYL)PYRIDINES

摘要

The polyfunctional 2,3- and 3,4-o-bis(chloromethyl)pyridines 3, produced vip cycloaddition of the oxazinones 2 with propargyl chloride and 1,4-dichloro-2-butyne, were used as precursors of various pyridine o-quinodimethane analogues. The 2,3- and 3,4-dimethylenepyridine systems were generated via reductive 1,4-elimination with iodide and trapped in situ with various dienophiles to form the tetrahydroquinoline and -isoquinoline type adducts. A regiospecific cycloaddition was observed for the 3,4-dimethylenepyridine system with electron-rich dienophiles, i.e. dihydrofuran and ethyl vinyl ether, in contrast to the reaction with methyl acrylate. Copyright (C) 1996 Elsevier Science Ltd. [References: 20]