THE STRUCTURE OF INTERMEDIATE PRODUCTS OF FRAGMENTATION OF 10-BROMODIHYDROCINCHONINE

10-Bromodihydrocinchonine 1d, similarly to analogical derivatives of o ther main cinchona alkaloids, transforms into nicinquine and isonicinq uine 2d formally loosing its C2 carbon atom in a form of formaldehyde. This reaction was found to proceed via the so-far unstudied intermedi ate compounds (5a) 4-S-(Z-propenyl)- and (5) 7-S-(quinolyl-4)-8-oxa-1- R-azabicyclo[4.3.0]nonane which at the same time are products of a nov el rearrangement of the parent cinchonine. The stenostructure of these compounds was determined using, mainly, NMR techniques. The energy mi nima of conformers 5 and 5a were supported by molecular mechanics calc ulations. The mechanisms for the 1d --> 5 --> 2d sequence have been di scussed. The alkaloid 5 is sterically preferred to its Z-isomer. The a ccompanying nucleophilic substitution (1d --> 6) and elimination (1d - -> 7) are also stereospecific. (C) 1998 Elsevier Science B.V.