α-Pyrones. Part 4. Synthesis of 3-benzoylamino-6-(indol-2-yl)pyran-2-ones and their rearrangement to substituted azepino[1,2-a]indole-6-ones: unusual neighbouring group participation

Abstract

6-(2-Nitrostyryl)pyran-2-ones 3 are converted into 6-(indol-2-yl)pyran-2-ones 4 by reduction of the nitro group with triethyl phosphite and consequent addition of the nitrene intermediate to the styryl double bond. Compounds 4 undergo a rather unusual, base-catalysed, rearrangement leading to azepino[1,2-a] indol-6-ones 5.