Picolyl chloride → 2-Pyridin-2-ylmethyl-piperazine-1,2,4-tricarboxylic acid 1-benzyl ester 4-tert-butyl ester 2-methyl ester

Participants

Reaction Steps

A stirred solution of piperazine-1,2,4-tricarboxylic acid 1-benzyl ester 4-tert-butyl ester 2-methyl ester (200 g, 529 mol), prepared as described by Bigge et al. (Tetrahedron Let. 1989, 30, 5193), in tetrahydrofuran (200 mL) and DMF (1.5 L) was cooled to about −78° C., and a 0.5 M solution of potassium bis(trimethylsilyl)amide in THF (1.27 L) was added. After the above solution had stirred for about one hour, the free base of 2-picolyl chloride was generated by extracting the corresponding hydrochloride salt (217 g, 1.32 mol) from saturated sodium bicarbonate solution with methylene chloride. The combined organic extracts were dried (MgSO4), concentrated, immediately dissolved in DMF (100 mL), and then added dropwise to the enolate containing solution. The reaction was stirred for about 4 hours at about −78° C., then slowly warmed to room temperature and stirred overnight The toluene and THF were removed under reduced pressure. The residue was extracted from water (1.5 L) with ethyl acetate (3×1 L), the combined extracts were then washed with water (1.5 L), dried (MgSO4) and then concentrated in vacuo to give 240 g of crude product of the title compound of part 3-A which was carried on to the next step: +APcI MS (M+H)+ 470, (M−tBu+H) 436; 1H NMR=400 MHz (methanol-d4) δ: 8.4 (arom, m, 1H), 7.65-7.2 (arom, m, 7H), 6.94 (arom, m, 1H), 5.18 (CbzNCHH, m, 1H), 5.05 (CbzNCHH, m, 1H), 2.54 (m, 1H), 1.41 (Boc, s, 9H).

Provenance & Evidence