Highly stereoselective synthesis of 3-amino-3,6-dideoxy-aldohexoses by tin triflate mediated aldol condensation reaction of tricarbonyl iron α-aminodienone complexes.: Total synthesis of multiprotected mycosamine.

The divalent tin enol ether of the racemic N-BOC alpha-aminodienone tricarbonyliron complex 4 reacts with both enantiomers of protected lactaldehydes to predominantly yield one optically active ketol diastereoisomer (45 %). From the enantiomerically pure complex (S)-(+)-4 and (R)-(+) tert butyldimethylsilyloxylactaldehyde this ketol is obtained almost alone (isolated 86 %). From there, the multi-protected 3-amino-3,6-dideoxy-D-aldohexose mycosamine is obtained in a few high yielding steps (decomplexation, stereospecific reduction to a 1,3-diol, transformation into a diacetate and ozonolysis; absolute configurations S,S,SR). By reduction of the ketol before decomplexation, the stereochemistry of the reaction is completely reversed (control by the Fe(CO)(3) and nor by the hydroxyl group), giving also access to the R,S,SR series, (Structures determined by X-ray diffraction). (C) 1999 Elsevier Science Ltd. All rights reserved.