Utilization of industrial waste materials. Part 14.† Synthesis of β-amino alcohols and thiols with a 2-azabicyclo[3.3.0]octane backbone and their application in enantioselective catalysis
New, chiral β-tert-amino tert-alcohols have been synthesized from the enantiomerically pure sec-amine (all-R)-1b via the new glycine, alanine and phenylglycine derivatives 2–6. Grignard additions to these esters provided the new rigid amino alcohols 7–11 in fair yields. The absolute configurations of the stereogenic centers, which arose during the alkylation step, were assigned by an independent route leading to some of the optical antipodes of 7–10. Condensation of enantiomerically pure β-amino alcohols 13a–g, 16 and 17 with γ-ketoester rac-12 afforded the N,O-acetals 14a–g, 18 and 19, which were subsequently reduced to the β-tert-amino alcohols 10a,c and 15a–g. X-Ray analysis of compound 19 was performed to verify the stereochemistry observed by chemical correlation. The nucleophilic ring opening of enantiomerically pure styrene oxide by amine 1b resulted in the formation of regioisomeric amino alcohols 9a, 21a, and 10a, 21b. Amino thiol derivatives 22 and 25a,b were prepared by treatment of 10a and 15a,b, respectively, with methanesulfonyl chloride followed by regio- and stereoselective cleavage of the in situ formed aziridinium ions with potassium thioacetate. Reduction of these compounds to thiols 23 and 26a,b and subsequent oxidation afforded amino disulfides 24 and 27a,b. Finally, the bicyclic β-amino alcohols and thiols were used as chiral ligands in the enantioselective addition of diethylzinc to benzaldehyde and ee values up to 96% were found.