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Study of the acid-catalyzed isomerization of dihydroveatchine.

A study of the acid-catalyzed isomerization of dihydroveatchine (5) resulted in the isolation of a single major compound, the aldehyde 6. Structure 6 has been derived from its spectral data. Reduction of 6 with NaBH4 gave compound 7, which was characterized through detailed NMR studies including 1D, 2D, and selective INEPT experiments, as well as preparation of its mono- and bis(p-nitrobenzoyl) derivatives 8 and 9. A plausible mechanism for the formation of 6, derived from the spectral data of the isomerized product obtained by deuterium labeling, is reported. Interestingly, the acid-catalyzed isomerization products of the allylic alcohols garryfoline (1) and dihydroveatchine (5) are different and appear to be dependent on the configurational orientation of the C(15) hydroxyl group. Unambiguous NMR chemical shift assignments for 5 are also reported.