Alternative tandem cyclisation pathways in the reaction between imines and enones. Issue 8 (25th February 2016)

• Record Type: Journal Article
• Authors: Girling, P. Ricardo; Batsanov, Andrei S.; Calow, Adam D.J.; Shen, Hong C.; Whiting, Andrew
• Is Part Of: Tetrahedron. Volume 72:Issue 8(2016)
• Page Start: 1105
• Page End: 1113
• Publication Date: 2016-02-25
• Subjects: Aza-Diels–Alder -- Lewis-acid -- Homogeneous catalysis -- Cycloaddition -- Dihydropyridine -- Piperidenone; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2016.01.006
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: Dihydroisoquinoline reacts with Danishefsky's diene under Lewis acidic conditions or neat, to give low to moderate yields of the formal aza-Diels–Alder, [4+2]-cycloadduct. However, using methoxyvinyl methylketone with Lewis acid catalysis does not give the aza-Diels–Alder adduct, rather a formal [2+2+2]-cycloaddition occurs to provide access to a diacetyl dihydropyridine. Increased Lewis acid loading results in reduced dihydropyridine formation, and instead, a trimerisation reaction of the methoxyvinyl methyl ketone occurs, to give 1, 3, 5-triacetylbenzene from a different formal [2+2+2]-cycloaddition. The formal [4+2]-cycloaddition reaction of methoxyvinyl methylketone requires a cyclic imine in order to form the dihydropyridine because the reaction with acyclic imines produced a dihydropyridine from a formal [1+2+1+2]-cycloaddition. Evidence resulting from the isolation of reaction intermediates and in situ spectroscopic studies, shows that the reaction between 3, 4-dihydroisoquinoline and methyl vinyl ketone, catalysed by oxy-philic Lewis acids, proceeds via a Mannich-Michael pathway and an imminium ion species. All reactions occur by one-pot cascade routes. Graphical abstract: