Highly stereoselective total synthesis of multiply protected 3-amino-3,6-dideoxyaldohexoses (mycosamine/mycaminose) by aldol condensation reaction, mediated by tin triflate, of tricarbonyliron/alpha-amimodienone complexes

The divalent tin enol ether of the racemic complex between N-BOC-alpha -ami noheptadienone and tricarbonyliron reacts with both enantiomers of protecte d lactaldehydes to yield predominantly one optically active, easily isolabl e ketol diastereoisomer (45%). From the enantiomerically pure (S)-(+) compl ex and (R)-(+)-tert-butyldimethylsilyloxylactaldehyde, the major ketol is o btained almost exclusively (isolated yield 86%). From there, the multiply p rotected 3-amino-3,6-dideoxy-d-aldohexose mycosamine is obtained in a few h igh-yield steps (decomplexation, stereospecific reduction to an anti-1,3-di ol, transformation into a diacetate and ozonolysis; absolute configurations S,S,S,R). Reduction of the ketol before decomplexation completely reverses the stereochemistry of the reaction [control by the Fe(CO)(3) and not by t he hydroxy group --> syn-diol], also giving access to the (R,S,S,R) series (configuration of the N,N-dimethylated mycaminose). The key structures were determined by X-ray diffraction.