Chemistry of acronycine. IX. Formation of dimers of noracronycine--mechanistic studies.

The mechanisms of two acid-mediated coupling reactions of noracronycine (2) have been studied using deuterium-labeled acids. Dimerization of noracronycine (2) using D2SO4 afforded AB-1-d4 (8), whereas coupling 2 and dihydronoracronycine (3) in 10N DCl/MeOD (1:2.5) afforded dihydro AB-2-d8 (15). In addition, in the dimerization reaction of 2 using D2SO4-CH3OD (1:1) followed by dilution with D2O, AB-1-d16 (19) was obtained instead of 8. Initial protonation at the C2 position of noracronycine (2) was verified during these studies.