SYNTHESIS OF (2S,4R,5R)-4,5,6-TRIHYDROXYNORLEUCINE AND 5-HYDROXYNORVALINE FROM PRECURSORS OBTAINED BY AN UNUSUAL REARRANGEMENT IN A 5,6-DIHYDRO-2-PYRONE

dene-2,3-dideoxy-D-erythro-hex-2-enono-1,5-lactone (2), readily prepar ed from D-glucosamine, undergoes a rearrangement on treatment with tin (IV) chloride which leads to 3-acetamido-2-pyrone (3) and -4,6-O-formy lidene-D-threo-hex-2-enono-1,5-lactone (4). A mechanism is proposed fo r this unusual rearrangement, which was not observed for other analogo us hex-2-enono-1,5-lactones. For example, the 2-acetoxy analog of 2 yl idene-3-deoxy-D-erythro-hex-2-enono-1,5-lactone, 7) was synthesized an d treated with tin(IV) chloride affording 3-acetoxy-6-chloromethyl-2-p yrone (8) as main product. The 2-pyrone derivatives 3 and 4 are conven ient precursors for the synthesis of 5-hydroxynorvaline (12) and (2S,4 R,5R,)-4,5,6-trihydroxynorleucine (14), respectively. The latter was p repared by diastereoselective hydrogenation of 4, followed by deprotec tion. Copyright (C) 1996 Elsevier Science Ltd