Glycals in Organic Synthesis: A Systematic Strategy for the Preparation of Uncommon Piperidine 1,2‐Dideoxy‐L‐azasugars and 2‐Deoxy‐1,5‐anhydro‐L‐hexitols

Abstract

AbstractA systematic synthetic strategy has been developed for producing uncommon piperidine 1,2‐dideoxy‐L‐azasugars. This method involves the formation of open intermediates such as 2, 7, and 10 easily by ring‐opening of D‐glycals with aqueous mercury(II) acetate/sodium borohydride. A concise sequence of regioselective amination and cyclization reactions then allowed us to prepare the cyclic compounds 5a and 5b, L enantiomers of naturally occurring fagomine congeners such as 3‐epi‐fagomine (II) and 3,4‐di‐epi‐fagomine (III), from D‐glucal and D‐galactal, respectively. The unnatural 3,4‐di‐epi‐6‐deoxyfagomine 9 was obtained from L‐rhamnal by the same reaction sequence. This straightforward chemistry has been shown to be useful for preparing glycosyl derivatives of 1,2‐dideoxy‐L‐azasugars starting from glycosyl glycals such as D‐lactal, D‐cellobial, D‐maltal, and D‐melibial, thus avoiding the usually lengthy glycosylation procedures. The flexibility of our protocol has been demonstrated by the easy conversion of the above‐described open intermediates into uncommon 2‐deoxy‐1,5‐anhydro‐L‐hexitols, never previously described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)