Concise, diastereoconvergent synthesis of endiandric-type tetracycles by iterative cross coupling

Abstract

Both fused and bridged tetracyclic scaffolds characteristic of endiandric acid-type natural products have been prepared in just seven steps each (longest linear sequence) from Burke's commercial cis-2-bromovinylboronic acid MIDA ester. Three iterative Suzuki–Miyaura couplings using MIDA boronates, including the first such example of a Z–Z coupling, trigger an 8π/6π-electrocyclization cascade. The mixture of endo and exo bicycles thus formed are elaborated into tetracycles via Horner–Wadsworth–Emmons and Diels–Alder reactions. In the process, the endo and exo diastereomers interconvert to ultimately deliver the desired products.