1: 71 percent / Ph3P, diethyl azodicarboxylate / tetrahydrofuran / 26 h / Ambient temperature 2: 83 percent / N2H4*H2O / methanol / 21.5 h / Heating 3: diethyl ether / 1) 0 deg C, 1 h, 2) rt, 19.5 h 4: 97 percent / 2 M KOH / methanol / 4 h / Ambient temperature 5: 83 percent / Ac2O / tetrahydrofuran / 120 h / Ambient temperature 6: 13 percent / air / various solvent(s) / 2 h / Heating 7: 54 percent / Ph3P / 1.5 h / Heating View Scheme

oxygen; triethylamine in toluene T=90°C; 8 h; Green chemistry; chemoselective reaction;

C51H41P2Ru(1+)*C32H12BF24(1-) in toluene T=20°C; 4 h;

carbon monoxide; [Rh(CO)2(Me2NCH2CH2NMe2)][RhCl2(CO)2] in tetrahydrofuran T=100°C; P=5171.62 Torr; 20 h; Autoclave;

triphenylphosphine; diethylazodicarboxylate in tetrahydrofuran 26 h; Ambient temperature;

hydrogen; palladium on activated charcoal in ethanol Ambient temperature;

With  diisobutylaluminium hydride  Yield given;