Total Synthesis and Structural Revision of the Cytotoxin Aruncin B

The sodium salts E-15 and Z-15 of the originally proposed dihydropyran acid structure of aruncin B (1) were prepared through ring-closing alkene metathesis (RCM) and ethoxyselenation-selenoxide elimination, but acid sensitivity of these salts, together with inconsistencies in the spectral data, suggested a significant structural misassignment. A β-iodo Morita-Baylis-Hillman reaction to give Z-iodo ester 24, followed by Sonogashira cross-coupling-5-exo-dig lactonization, provided concise access to a Z-γ-alkylidenebutenolide 18, which possessed data corresponding to those originally reported for aruncin B.