1: 72 percent / NaOH / dimethylformamide; acetone 2: 1.) N-methylmorpholine, isobutyl chloroformate / 1.) THF, -15 - -10 deg, 15 min., 2.) THF, DMF, a) -15 - -10 deg, 2h, b) RT, overnight 3: 86 percent / NaOH / dimethylformamide; acetone / 1 h / Ambient temperature 4: 1.) N-methylmorpholine, isobutyl chloroformate, 2.) N-methylmorpholine / 1.) THF, -15 - -10 deg, 15 min., 2.) THF, DMF, a) -15 - -10 deg, 2h, b) RT, overnight 5: 94 percent / CH2Cl2 / 0.5 h / Ambient temperature View Scheme