1: 100 percent / HCl gas / ethyl acetate / 0.05 h / 0 °C 2: 72 percent / Na(OAc)3BH, 4A MS / 1,2-dichloro-ethane / 4 h / 0 - 20 °C / tandem reductive alkylation-cyclization of amines with various aldehydes and ketones to give 2m3-diketopiperazines 3: 81 percent / aq. HCl / 5 h / Heating View Scheme

1: 100 percent / HCl gas / ethyl acetate / 0.05 h / 0 °C 2: acetophenone, Na(OAc)3BH, 4A MS / 1,2-dichloro-ethane / 1.) 0 deg C, 30 min, 2.) room temperature, 4 h View Scheme