Lithium borohydride, reduction imides

Hydroxymethylpyrazines may be prepared by reduction of carboxylic acid derivatives. Thus reduction of 2-amino-3-methoxycarbonylpyrazine with lithium aluminum hydride in tetrahydrofuran gave 2-amino-3-hydroxymethylpyrazine (1074, 1075) the imide from 23-dicarboxypyrazine (20) with sodium borohydride in tetrahydrofuran gave 2-carbamoyl-3-hydroxymethylpyrazine (21), and the methylcarbamoyl analogue was prepared similarly (1076). 

When the mixed anhydride between 4-ethyl-4-pentenoic acid and pivalic acid (prepared using pivaloyl chloride on the pentenoic acid) was treated with the lithium salt of (i )-4-benzyl-2-oxazolidinone an imide was formed where one (the bottom as drawn) face is encumbered by the bulky benzyl group. Thus, cyanoeth-ylation occurred with diastereoselectivity, and a single isomer was isolated. Reduction of the imide with sodium borohydride (NaBU,) then resulted in the formation of the primary alcohol, and the latter was protected as the f-butyldiphenylsilyl (TBDPS)... 

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