Abstract
Brønsted acid promoted reversible dimerization of myrmicarin 215B leads to formation of a new heptacyclic product, isomyrmicarin 430B, that possesses a C1,C2-trans,C2,C3-trans-substituted cyclopentane ring. Mechanistic studies illustrate that isomyrmicarin 430B arises by isomerization of isomyrmicarin 430A via fragmentation to tricyclic azafulvenium ions. Factors influencing the structure of heptacyclic isomyrmicarin products and potential relevance of this reversible vinyl pyrroloindolizine dimerization to the biosynthesis of complex myrmicarins are discussed.