Total Syntheses of Indole Alkaloids: On the Syntheses of Yohimbine and Ergot type of Alkaloids

A general total synthetic methodology for indole alkaloids via the route involving reductive photocyclization of enamides has been developed. Acylation of imines such as harmalane and tricyclic imine with either p-methoxybenzoyl or 3-furoyl chloride followed by reductive photocyclization furnished the compounds having skeletal structures of indole alkaloids, yohimbines and ergolines. They were then readily converted, upon modification of either methoxylated dihydrobenzene or dihydrofuran ring to respective alkaloids including yohimbine, alloyohimbine, deserpidine, and 19, 20-dehydroyohimbine in one group and lysergic acids, elymoclavine, agroclavine, lysergols, lysergines, and fumigaclavines in another group.