REFORMATSKY REACTION ON ALPHA-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

A novel cycloaromatization reaction leading to substituted and annelated ethyl 2-hydroxy-6-(methylthio) benzoates 4 by condensation of a-oxo ketene dithioacetals with an excess of Reformatsky reagent from ethyl bromoacetate through intermediate dienes 3 has been described. The reaction has also been extended for the synthesis of substituted ethyl 3-hydroxy-5-(methyl thio)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. © 1990, American Chemical Society. All rights reserved.