Facile synthesis and spectroscopic elucidation of 4,11-bis(dehydroxy)-bipolaroamide

A new diketopiperazine was formed by facile condensation of the artificial 2-indoline carboxylic acid. This highly crystalline compound was characterized by NMR-spectroscopy as well as X-ray crystallography. Spectroscopic data of the new pentacyclic diketopiperazine revealed further evidence that the phosphite-promoted coupling used is free of racemization or inversion. These stereochemical results are important for this advanced reaction and may lead to a key step in the total synthesis of many natural products. The dimerized 2-indoline carboxylic acid described herein was chosen to be a model system for structure and reaction studies on route to the favored rostratines.