Supply structures for H through K. Given : " An aldohexose" overset(NH_(2)OH"/base")(to)H overset(Ac_(2)O"/"NaOAc)(to)I overset(-HOAC)(to)J overset(NaOMe"/"MeOH)(to)K. Explain the last step. What is net structural change. Name this overall method. Discuss the possibility of epimer formation.

Supply structures for H through K. Given : " An aldohexose" overset(N

1.	Supply structures for H through K. Given : " An aldohexose" overset(NH_(2)OH"/base")(to)H overset(Ac_(2)O"/"NaOAc)(to)I overset(-HOAC)(to)J overset(NaOMe"/"MeOH)(to)K. Explain the last step. What is net structural change. Name this overall method. Discuss the possibility of epimer formation.
Answer» Solution :H is an oxime `HOCH_(2)(CHOH)_(4)CH=NOH`, I is the COMPLETELY acetylated oxime, `AcOCH_(2)(CHOAc)_(4)CH=NOAc` that loses 1 mole of HOAc to form J, `AcOCH_(2)(CHOAc)_(4)C EQUIV N, K` is an aldopentose, `HOCH_(2)(CHOH)_(3)CHO`. The acetates undergo TRANSESTERIFICATION to give methyl acetate freeing all the sugar OH.s. This is followed by reversal of HCN addition. There is loss of one C from the carbon chain. Wohl degradation. The `alpha-CHOH` becomes the `-CH=O` without any configurational changes of the other chiral carbons. Thus no epimers are formed.