Asymmetric conversions of 10-bromo-10,11-dihydroquinines into 8-oxa-1-azabicyclo[4.3.0]nonane derivatives and related compounds

Some transformations of (10R)- and (10S)-bromo-10,11-dihydroquinine 2a and 2b have been investigated in order to obtain insights into their unexplored chirality. The (10R)-diastereomer 2a converts stereoselectively into (4S)-(E-propenyl)-(6S,7R)-(6-methoxy-quinol-4-yl)-8-oxa-(1R)-azabicyclo[4.3.0]nonane 10, which is the product of a novel rearrangement of the parent quinine 1 and displays the N(1)-(S)-configuration (10a) in the solid state. The (10S)-diastereomer 2b afforded 10 and its (Z)-propenyl isomer 15 (in the ratio 55:45), as well as (Z)-3,10-didehydro-10,11-dihydro-quinine 19. On treatment with acid the alkaloid 10 yields [(4S)-(E)-propenyl)-(2S)-piperidinyl]-6-methoxyquinoline-(αR)-methanol 12. Closure of the oxazolidine ring in 12 gives 14, the 9,9-dimethyl-derivative of 10, with the N(1) configuration inverted. The molecular structures of 10a and 14, determined by X-ray diffraction, show their similar conformations except for the axial (E)-propenyl substituent, disordered in two orientations in 10a and ordered in another position in 14. [Copyright &y& Elsevier]