1: LiB(Et)3H / tetrahydrofuran / 1 h / 0 °C 2: 1.) LDA, HMPT, 2.) P(OEt)3, O2 / 1.) THF, hexane, from -70 to -60 deg C, 1 h, 2.) THF, hexane, -70 deg C View Scheme

With  dimethyl sulfoxide; trifluoroacetic anhydride in  dichloromethane T=-60°C; 1.5 h;  Yield given;   

Multi-step reaction with 2 steps 1: tetrahydrofuran / 1 h / 0 - 5 °C2: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C  

Multi-step reaction with 3 steps 1: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C2: tetrahydrofuran / 1 h / 0 - 5 °C3: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C  

Multi-step reaction with 5 steps 1: 170 °C2: 89.2 percent / LiB(Et)3H / tetrahydrofuran / 1 h / 0 °C3: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C4: tetrahydrofuran / 1 h / 0 - 5 °C5: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C  

Multi-step reaction with 6 steps 1: aq. Ba(OH)2 / ethanol / 0.33 h / 70 °C2: 170 °C3: 89.2 percent / LiB(Et)3H / tetrahydrofuran / 1 h / 0 °C4: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C5: tetrahydrofuran / 1 h / 0 - 5 °C6: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C  

Multi-step reaction with 4 steps 1: 89.2 percent / LiB(Et)3H / tetrahydrofuran / 1 h / 0 °C2: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C3: tetrahydrofuran / 1 h / 0 - 5 °C4: trifluoroacetic anhydride, DMSO / CH2Cl2 / 1.5 h / -60 °C