Formation of 2,3-dihydro-4(1H)-quinolones and related compounds via Fries-type acid-catalysed rearrangement of 1-arylazetidin-2-ones

Abstract

A variety of 1-arylazetidin-2-ones were treated with trifluoroacetic acid under reflux, methanesulphonic acid at 100 °C, or conc. sulphuric acid to give the corresponding 2,3-dihydro-4(1H)-quinolones via acyl migration and N–CO fission. In the case of 1-(3-substituted phenyl)azetidin-2-ones, two positional isomeric products, 5- and 7-substituted 2,3-dihydro-4(1H)-quinolones were obtained. 4-Methyl-, 4-ethoxycarbonyl-, and 4-piperidin-2yl-1-arylazetidin-2-ones and their analogues were also converted into the corresponding 2-substituted 2,3dihydro-4(1H)-quinolones under acidic conditions. The 3-substituted 1-phenylazetidin-2-ones (36) and (37) were converted into the furo[3,2-c]quinoline systems (38) and (40), respectively, by application of this method.