A solution of (S)-7-hydroxy-6-nitro-3,4-dihydro-1H-isoquinoline-2,3-dicarboxylic acid 2-tert-butyl ester 3-methyl ester (3.0 g, 8.5 mmol), resin-bound triphenylphosphine (17 mmol), [4-(3,4-dichloro-benzyloxy)-phenyl]-hydroxy-acetic acid 3,4-dichloro-benzyl ester (13.0 mmol) in DCM-THF (1-1, 80 mL) was cooled to 0° C. To this solution was added DIAD (13.0 mmol) and the mixture was agitated for 10 min at 0° C. and the mixture was slowly allowed to warm up to r.t. and agitated for 16 h. The reaction mixture was filtered, concentrated and the residue passed over a plug of silica-gel hexanes-ethyl acetate (9:1). The resulting residue was dissolved in glacial acetic acid (65 mL) and iron powder (170 mmol) added. The resulting mixture was heated at 100° C. for 1 h. The mixture was poured onto water and EtOAc. The organic layer was washed with water, brine, saturated sodium bicarbonate solution and dried over sodium sulfate. The solution was concentrated under reduced pressure to give the desired product. This crude product was purified by silica gel column chromatography using hexanes-ethyl acetate (7:3) to afford (7S)-3-[4-(3,4-dichloro-benzyloxy)-phenyl]-2-oxo-1,2,3,5,7,8-hexahydro-4-oxa-1,6-diaza-anthracene-6,7-dicarboxylic acid 6-tert-butyl ester 7-methyl ester (1.6 g). LC-MS (m/z) 614.
