Tetrakistriphenylphosphine palladium (778 mg, 673 mmol, 0.04 equiv) was added to a deoxygenated solution of (7S, 10R)-7,8,9,10-tetrahydro-2,9,9-trimethoxy-7-methyl-6,10-phenanthridinediol 6-(trifluoromethanesulfonate) (13, 7.60 g, 16.8 mmol, 1 equiv) and triethylamine (9.40 mL, 67.3 mmol, 4.00 equiv) in dioxane (300 mL) at 23° C. The resulting solution was deoxygenated by alternately evacuating the reaction vessel and flushing with argon (5×). Formic acid (1.70 mL, 43.8 mmol, 2.63 equiv) was added slowly over 5 min via syringe and the resulting solution was heated at reflux for 20 min, then was allowed to cool to 23° C. The reaction mixture was partitioned between saturated aqueous sodium chloride solution (300 mL) and ethyl acetate (300 mL). The aqueous layer was separated and further extracted with ethyl acetate (2×300 mL). The combined organic layers were dried over sodium sulfate and were concentrated in vacuo. The residue was purified by flash column chromatography (ether initially, grading to 20% ethyl acetate-ether) to provide (7S, 10R)-7,8,9,10-tetrahydro-2,9,9-trimethoxy-7-methyl-10-phenanthridinol (15) as a white foam (mp 135°-136° C., 4.94 g, 97%).
