Formaldehyde → (S)-3-[4-(3,4-dichloro-benzyloxy)-phenyl]-2,3,8,9-tetrahydro-6H-[1,4]dioxino[2,3-g]isoquinoline-7,8-dicarboxylic acid 7-tert-butyl ester 8-methyl ester

Participants

Reaction Conditions

Reaction Steps

(S)-2-tert-Butoxycarbonylamino-3-{2-[4-(3,4-dichloro-benzyloxy)-phenyl]-2,3-dihydro-benzo[1,4]dioxin-6-yl}-propionic acid methyl ester (2.1 g) was deprotected according to General Procedure C. The resulting material was dissolved in dioxane (20 mL) and TFA (4 mL) and solid paraformaldehyde (300 mg) added. The reaction mixture was heated for 2 h at 60° C. and concentrated. The resulting material was dissolved in DCM and aqueous sodium bicarbonate and ditert-butyl pyrocarbonate (1.5 g) added. The layers of the reaction mixture were separated and the aqueous layer was extracted twice with 50. mL of DCM. The combined organic extracts were dried over sodium sulfate, filtered, and concentrated to provide a yellow solid. The residue was purified by silica gel chromatography (10/90 to 30/70 ethyl acetate/hexanes in 10% increments) to obtain the desired product. 1H NMR (400 MHz, CDCl3): 7.54 (d, 1H), 7.45 (d, 1H), 7.32 (d, 2H), 7.24 (m, 2H), 6.96 (d, 2H), 6.77 (s, 1H), 6.72 (d, 2H), 5.04 (m, 1H), 5.02 (s, 2H), 4.73 (m, 1H), 4.60 (m, 1H), 4.40 (m, 1H), 4.26 (m, 1H), 3.97 (m, 1H), 3.64 (d, 3H), 3.02-3.20 (m, 2H), 1.54 and 1.44 (s, 9H).

Provenance & Evidence