5 h; Inert atmosphereReflux;

1.1: 5 h / Inert atmosphere; Reflux 2.1: toluene-4-sulfonic acid; trimethyl orthoformate / 5 h / 20 °C / Inert atmosphere 3.1: water; sodium hydroxide / 20 °C 4.1: N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide / dichloromethane / 0.33 h / 20 °C / Inert atmosphere 4.2: 20 °C / Inert atmosphere 5.1: water; trifluoroacetic acid / 20 °C / Inert atmosphere View Scheme

triethylamine in acetonitrile Reflux;

triethylamine in acetonitrile 3 h; Heating;

1.1: 5 h / Inert atmosphere; Reflux 2.1: toluene-4-sulfonic acid; trimethyl orthoformate / 5 h / 20 °C / Inert atmosphere 3.1: water; sodium hydroxide / 20 °C 4.1: N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide / dichloromethane / 0.33 h / 20 °C / Inert atmosphere 4.2: 20 °C / Inert atmosphere 5.1: water; trifluoroacetic acid / 20 °C / Inert atmosphere View Scheme

1: 2.6 g / 4 h / Heating 2: 80 percent / p-TsOH; methyl orthoformate / toluene / 4 h View Scheme

4 h; Heating;

1.5 h; Heating;