Synthetic Strategies toward Lysergic Acid Diethylamide: Ergoline Synthesis via α-Arylation, Borrowing Hydrogen Alkylation, and C-H Insertion.

A novel seven-step formal synthesis of LSD has been developed, focusing on connecting the A- and D-rings first and then bridging the B- and D-rings last. The synthesis uses cross-coupling, intramolecular α-arylation, borrowing hydrogen alkylation, and rhodium-catalyzed C-H insertion to form the tetracyclic ergoline core. The methods enable the first introduction of substitutions on the C-ring, though each strategy faces unique challenges when elaborating to ergoline natural products. These findings provide insights that will guide future synthetic strategies toward ergolines and related compounds.

Study at a glance

Abstract

Lysergic acid diethylamide (LSD), a semisynthetic ergoline alkaloid analogue and hallucinogen, is a potent psychoplastogen with promising therapeutic potential. While a variety of synthetic strategies for accessing ergoline alkaloids have emerged, the complexity of the tetracyclic ring system results in distinct challenges in preparing analogues with novel substitution patterns. Methods of modulating the hallucinogenic activity of LSD by functionalization at previously inaccessible positions are of continued interest, and efficient syntheses of the ergoline scaffold are integral toward this purpose. Here, we report novel C-C bond forming strategies for preparing the ergoline tetracyclic core, focusing on the relatively unexplored strategy of bridging the B- and D-ring systems last. Following cross-coupling to first join the A- and D-rings, we explored a variety of methods for establishing the C-ring, including intramolecular α-arylation, borrowing hydrogen alkylation, and rhodium-catalyzed C-H insertion. Our results led to a seven-step formal synthesis of LSD and the first methods for readily introducing substitution on the C-ring. These strategies are efficient for forming ergoline-like tetracyclic compounds and analogues, though they each face unique challenges associated with elaboration to ergoline natural products. Taken together, these studies provide important insights that will guide future synthetic strategies toward ergolines.