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

Abstract

The divalent tin enol ether of the racemic N-BOC α-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,S,R). By reduction of the ketol before decomplexation, the stereochemistry of the reaction is completely reversed (control by the Fe(CO) 3 and not by the hydroxyl group), giving also access to the R,S,S,R series. (Structures determined by X-ray diffraction).