The Stereoisomerization of <i>N</i>,<i>N</i>′-Diacyl Derivatives of Indigo

Abstract

Abstract The cis-isomers of N,N′-diacylindigo (e.g., cis-N,N′-diacetyl-, distearoyl-, dibenzoyl-, and bis(3,5-dinitrobenzoyl)-indigo) were found to separate out in a crystalline form from a solution of the corresponding trans-isomer upon irradiation. The kinetics of the cis-to-trans isomerization of these four cis-N,N′-diacylindigos was studied, the relative rates being 7.9, 11.0, 1.0, and 5.1 respectively. Several amines were found to accelerate the cis-to-trans isomerization in the order of: Et2NH&amp;gt;PrNH2&amp;gt;Et3N&amp;gt;i-Pr2NH in the case of cis-N,N′-diacetylindigo and in the order of: Et2NH&amp;gt;i-Pr2NH&amp;gt;PrNH2&amp;gt;Et3N in the case of cis-N,N′-dibenzoylindigo.