Propylamine → Phenylmethyl N-propylcarbamate

Cbz Protection A solution of propylamine (9.0 g, 152.4 mmol) and triethylamine (15.4 g, 152.4 mmol) in methylene chloride (350 mL) was cooled to 0° C. and treated with benzyl chloroformate (20.0 g, 117.2 mmol). Upon stirring at 0° C. for 1 hour the reaction was warmed to ambient temperature and quenched with 1N HCl. The reaction was partitioned between 1N HCl and methylene chloride. The organics were washed with 1N HCl, water and brine. The combined organics were dried over sodium sulfate, filtered and evaporated in vacuo to give benzyl propylcarbamate as a clear oil. 1H NMR (400 MHz, CDCl3) δ 7.37 (m, 5H), 5.10 (s, 2H), 4.77 (bs, 1H), 3.16 (q, J=6.5 Hz, 2H), 1.52 (m, 2H), 0.92 (t, J=7.5 Hz, 3H). Step B: Alkylation A solution of benzyl propylcarbamate (20.8 g, 107.9 mmol) in DMF (200 mL) was cooled to 0° C. and treated with sodium hydride (4.6 g, 194.2 mmol). The reaction was stirred to 0° C. for 15 minutes and subsequently treated with crotyl bromide (17.5 g, 129.5 mmol). The reaction was warmed to ambient temperature and stirred for 16 hours. The reaction was quenched with ammonium chloride solution and partitioned between water and ether. The organics were washed with water (4×) and brine, dried over sodium sulfate, filtered and evaporated in vacuo. Flash chromatography (silica, 0-10% EtOAc/hexanes) gave benzyl (2E)-but-2-enyl(propyl)carbamate as a clear oil. 1H NMR (400 MHz, CDCl3) δ 7.35 (m, 5H), 5.57 (bt, 1H), 5.42 (bs, 1H), 5.13 (s, 2H), 3.82 (bm, 2H), 3.19 (bs, 2H), 1.68 (bs, 3H), 1.54 (bs, 2H), 0.87 (bs, 3H). Step C: Cyclopropanation A solution of benzyl (2E)-but-2-enyl(propyl)carbamate (5.0 g, 20.2 mmol) in methylene chloride (120 mL) was cooled to 0° C. and treated with diethylzinc (12.48 g, 101 mmol) followed by diiodomethane (54.1 g, 202 mmol). The reaction was warmed to ambient temperature and stirred for 16 hours. The reaction was quenched with saturated ammonium chloride solution and partitioned between methylene chloride and saturated sodium bicarbonate solution. The organics were dried over sodium sulfate, filtered and evaporated in vacuo. Flash chromatography (10% EtOAc/hexanes) gave 5.16 g (96%) of benzyl (2-methylcyclopropyl)methyl(propyl)carbamate as a yellow oil. 1H NMR (400 MHz, CDCl3) δ 7.35 (m, 5H), 5.13 (s, 2H), 3.16 (bm, 4H), 1.59 (bm, 2H), 1.01 (bs, 3H), 0.88 (bs, 3H), 0.68 (bs, 2H), 0.34 (bd, 1H), 0.22 (bs, 2H). Step D: Hydrogenation