Synthesis of the Tagetitoxin Core via Photo-Stevens Rearrangement

The core structure of the RNA polymerase inhibitor tagetitoxin has been synthesized by one-carbon ring expansion of bridged bicyclic monothioacetals. The key steps are intramolecular ylide formation by reaction between the sulfur atom and a pendant diazoester, followed by an efficient photochemical 1,2-rearrangement to give the desired 9-oxa-3-thiabicyclo[3.3.1]nonane ring system.