Carbon‐13 and proton two‐dimensional NMR study of diterpenoids of Coleus forskohlii

The stereochemical assignments of coleonol‐B (1), coleonol‐D (2) and coleosol (3) were accomplished by 2D 1H1H (COSY), 1H13C (hetero COSY), NOE difference NMR spectroscopic, stereospecific coupling constant and selective heteronuclear spin decoupling studies. The complete 13C chemical shift assignments of 2, 3 and coleol (4) were made for the first time. The earlier 1H chemical shift assignments were corrected and the stereostructure of coleonol‐D was reassigned.