Reformatsky Reaction on α-Oxo Ketene Dithioacetals: Synthesis of Substituted and Fused Ethyl 2-Hydroxy-6-(methylthio)benzoates, 6-(Methylthio)pyran-2-ones, and 6-(Methylthio)-2(1H)-pyridone Derivatives

Article abstract of DOI:10.1021/jo00308a015

A novel cycloaromatization reaction leading to substituted and annelated ethyl 2-hydroxy-6-(methylthio)benzoates 4 by condensation of α-oxo-ketene dithioacetals with an excess of Reformatsky reagent from ethyl bromoacetates through intermediate dienes 3 has been described.The reaction has also been extended for the synthesis of substituted ethyl 3-hydroxy-5-(methylthio)stilbenecarboxylates 9 by using cinnamoyl ketene dithioacetals 8.A few of the benzoates 4 were desulfurized to the corresponding salicylate derivatives 5.Reaction of acyclic oxo ketene dithioacetals with ethyl(bromozincio)acetate in the presence of cuprous iodide afforded 4- (or 4,5-)substituted 6-(methylthio)pyran-2-ones 15 in moderate to good yields.A probable mechanism for the formation of 15 is suggested.Cyclization of the acyclic dienes 3 or the carbinols 10 with ammonium acetate in refluxing acetic acid afforded the corresponding 4- (or 4,5-)substituted 6-(methylthio)-2(1H)-pyridones 22.