1: 6-ethyl-2,2,5-trimethyl-4H-1,3-dioxin-4-one With lithium diisopropyl amide in tetrahydrofuran; pentane T=-78°C; 2: acetaldehyde in tetrahydrofuran; pentane aldol reaction; 0.333333 h; 3: With trifluoroacetic acid in tetrahydrofuran; pentane T=-78°C; 0.166667 h;

1.1: 92 percent / Ac2O; H2SO4 / 12 h / 0 °C 2.1: LDA / pentane; tetrahydrofuran / -78 °C 2.2: pentane; tetrahydrofuran / 0.33 h 2.3: TFA / pentane; tetrahydrofuran / 0.17 h / -78 °C View Scheme

1: triethylamine; sodium iodide; magnesium chloride 2: sulfuric acid; acetic anhydride / 0 °C 3: trifluoroacetic acid; lithium diisopropyl amide / tetrahydrofuran View Scheme

oxalyl dichloride; dimethyl sulfoxide; triethylamine in dichloromethane T=-78 - 0°C; Swern oxidation;

1: 4.00 g / oxalyl chloride; DMSO; triethylamine / CH2Cl2 / -78 - 0 °C 2: 83 percent / sodium methoxide / methanol / 0 °C View Scheme

1: 4.00 g / oxalyl chloride; DMSO; triethylamine / CH2Cl2 / -78 - 0 °C 2: 83 percent / sodium methoxide / methanol / 0 °C 3: 93 percent / CH2Cl2 / 2 h / 20 °C View Scheme