pyridinium p-toluenesulfonate; trimethyl orthoformate in dichloromethane 5 h; Heating;

1.1: n-BuLi / tetrahydrofuran; hexane / 12 h / 20 °C 1.2: 91 percent / KOH / tetrahydrofuran; hexane; methanol / 0.5 h / 20 °C 2.1: 20 percent / PPTS; CH(OMe)3 / 1,2-dichloro-ethane / 2 h / Heating View Scheme

1: 89 percent / AlCl3 / 20 h / 23 °C 2: 72.6 percent / acetylene / tetrahydrofuran; dimethylsulfoxide / 23 °C 3: 81.6 percent / PPTS; trimethyl orthoformate / CH2Cl2 / 5 h / Heating View Scheme

1: 89 percent / AlCl3 / 20 h / 23 °C 2: 72.6 percent / acetylene / tetrahydrofuran; dimethylsulfoxide / 23 °C 3: 81.6 percent / PPTS; trimethyl orthoformate / CH2Cl2 / 5 h / Heating View Scheme

pyridinium p-toluenesulfonate; trimethyl orthoformate in 1,2-dichloro-ethane 2 h; Heating;