Triacetoxyperiodinane → tert-butyl 7-chloro-3-formyl-3,4-dihydroisoquinoline-2(1H)-carboxylate

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Reaction Steps

While under nitrogen, a stirred solution of tert-butyl 7-chloro-3-(hydroxymethyl)-3,4-dihydroisoquinoline-2(1H)-carboxylate (Step 6, 270 mg, 0.907 mmol) in methylene chloride (11 mL) was cooled in an ice-water batch and treated dropwise with a solution of Dess-Martin periodinane (461 mg, 1.09 mmol) in methylene chloride (3 mL) over several minutes. The cooling bath was removed, and the resulting clear mixture was stirred at room temperature for 1.5 h. Once complete, the mixture was re-cooled in an ice-water bath, quenched portionwise with a 1:1 mixture of saturated aqueous Na2S2O3 and saturated aqueous NaHCO3 (20 mL total) and stirred for 10 min at room temperature. The layers were separated, the aqueous phase was re-extracted with methylene chloride (20 mL), and the combined organic phase was washed with saturated aqueous sodium chloride (10 mL), dried over Na2SO4 and concentrated under reduced pressure. Purification by silica gel chromatography (40 g column, 10-30% ethyl acetate in hexanes) gave tert-butyl 7-chloro-3-formyl-3,4-dihydroisoquinoline-2(1H)-carboxylate (162 mg, 60%) as a clear gum. 1H NMR (DMSO-d6, 400 MHz) δ 9.45 (bs, 1 H), 7.34 (m, 1 H), 7.26 (m, 2 H), 4.78 (m, ˜0.5 H), 4.64 (m, ˜0.5 H), 4.50 (m, 2 H), 3.21 (m, 1 H), 3.05 (m, 1 H), 1.46 (s, ˜4.5 H), 1.38 (s, ˜4.5 H) mixture of rotamers).

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