Synthesis of enantiopure 4-hydroxypipecolate and 4-hydroxylysine derivatives from a common...

tert-Butyl 2-substituted 4,6-dioxo-1-piperidinecarboxylates 4 have been prepared in good yield starting from Boc-Asp-O(t)Bu and other beta-amino acids. By analogy with chiral tetramic acids, their reduction by NaBH(4) in CH(2)Cl(2)/AcOH afforded the corresponding cis-4-hydroxy delta-lactams in good yield and stereoselectivity (68-98% de). In the absence of the A(1,3) strain (reduction of 6-substituted 2,4-dioxo-1-piperidines 7), the cis-4-hydroxy isomer was still obtained as the major product but the de values were consistently lower. 4-Hydroxy-6-oxo-1,2-piperidinedicarboxylate 2a, readily accessible from Boc-Asp-O(t)Bu (three steps, 63% overall yield), has proven to be an excellent building block for the synthesis of cis- and trans-4-hydroxypipecolates 17 and 24 (52 and 36% overall yield, respectively) and for the synthesis of a protected 4-hydroxylysine derivative 29 (41% overall yield).