THE INDOPHENINE REACTION REVISITED - PROPERTIES OF A SOLUBLE DIALKYL DERIVATIVE

The classical indophenine reaction of thiophene with isatin and sulfur ic acid has been reinvestigated using N-heptylisatin, which affords so luble reaction products amenable to chromatographic purification. An N MR analysis of the resulting indophenine blue (8) has shown it to be a mixture of all six possible geometric isomers (8a-f) of the previousl y assumed gross structure. The intermediacy of alcohol 11 in the forma tion of 8 is strongly supported. In addition, an indophenine analog (9 a) derived from only one thiophene unit is reported for the first time .