From (-)-quinic acid to 8-azabicyclo[3.2.1]octane framework:: Preparation of an enantiopure tropan-6α-ol

The carbon atom ring-insertion via pyrolysis of an alpha-diazo-beta-hydroxy ester intermediate, in turn obtained by reaction between ethyldiazoacetate and 3,4-O-isopropylidene-3(R),4(S)-dihydroxycyclohexanone 2, a chiron easily prepared through a five step sequence from D(-)-quinic acid 1, was the key step for the construction of the cycloheptanone derivative 8. Its transformation into azidosulfate 18 set the stage for the preparation of the N-protected 8-azabicyclo[3.2.1]octane derivative 22, which, to the best of our knowledge, has been never obtained in optically pure form, as well as the tropan-6 alpha-ol 24, obtained by reduction with LiAlH4. (C) 1999 Elsevier Science Ltd. All rights reserved.