The Biomimetic Synthesis and First Characterization of the (+)‐ and (−)‐Isocentrolobines, 2,6‐cis‐ and 2,6‐trans‐Disubstituted Tetrahydro‐2H‐pyrans

The four stereoisomers of the novel title compounds were prepared by oxidative cyclization of their enantiomerically pure diarylheptanoid precursors by means of the straightforward biomimetic approach presented in the preceding article. The isocentrolobines are the methoxy regioisomers of the natural (+)‐ and (−)‐centrolobines and were characterized for the first time. The synthetic procedure established the absolute configurations and the unambiguous correlation with the chiroptical data. The spectroscopic and the chiroptical data of the isocentrolobines are highly similar to those of the natural products. The single diagnostic parameter that would allow a immediate assignment in the presence of only one of the isomers is the higher melting point (ca. 50°) of the cis‐configured isocentrolobines.