Synthesis and Configuration of O -Acetyl Microgrewiapine A: Phantomization of O -Acetyl 6- epi -Microgrewiapine A.

The formation of O -acetyl microgrewiapine A is investigated. NMR data for the authentic sample derived from the natural product are corrected. Wholly synthetic samples, produced from reductive N -methylation of synthetic microcosamine A (to give synthetic microgrewiapine A) followed by O -acetylation, exhibit NMR data that are identical to those of the authentic sample. The previous report that this two-step transformation proceeds with epimerization at C-6 is thus shown to be in error: the purported sample of O -acetyl 6- epi -microgrewiapine A is structurally misassigned and is, in fact, O -acetyl microgrewiapine A. A plausible rationale for the structural misassignment is advanced.