1: 60 percent / p-toluenesulfonic acid / dimethylformamide / 48 h / Ambient temperature 2: 61 percent / silver triflate, 2,4,6-collidine / toluene; nitromethane / 0.25 h / -25 °C 3: 1.) 90 percent aqu. acetic acid, 2.) 0.2 M sodium methoxide / 1.) reflux, 30 min, 2.) methanol, 3 h, room temperature View Scheme

1: 60 percent / p-toluenesulfonic acid / dimethylformamide / 48 h / Ambient temperature 2: 61 percent / silver triflate, 2,4,6-collidine / toluene; nitromethane / 0.25 h / -25 °C 3: 1.) 90 percent aqu. acetic acid, 2.) 0.2 M sodium methoxide / 1.) reflux, 30 min, 2.) methanol, 3 h, room temperature View Scheme

toluene-4-sulfonic acid in N,N-dimethyl-formamide 48 h; Ambient temperature;