C([Li])CCC.C([Mg]Br)CCC.[CH:12]1([N:15]([CH2:23][C:24]2[CH:29]=[CH:28][C:27](Br)=[C:26]([Br:31])[CH:25]=2)[C:16](=[O:22])[O:17][C:18]([CH3:21])([CH3:20])[CH3:19])[CH2:14][CH2:13]1.CN([CH:35]=[O:36])C>C1(C)C=CC=CC=1>[Br:31][C:26]1[CH:25]=[C:24]([CH:29]=[C:28]([CH:35]=[O:36])[CH:27]=1)[CH2:23][N:15]([CH:12]1[CH2:14][CH2:13]1)[C:16](=[O:22])[O:17][C:18]([CH3:21])([CH3:20])[CH3:19]To a toluene (0.1 M) solution of n-butyl lithium (2.5 M in hexanes, 1.2 eq.) was added at −10° C. n-butyl magnesium bromide (2.0 M in THF, 0.4 eq.). The resulting suspension was stirred at −10° C. for 20 min before tert-butyl cyclopropyl(3,4-dibromobenzyl)carbamate (1 eq., Amine 77, Step 2) was added. The now yellow-red suspension was stirred at 0° C. for 30 min before DMF (30 eq.) was added dropwise neat at −78° C. The reaction mixture was allowed to warm slowly to RT over 3 h. The now black suspension was quenched with 10% aq. HCl and then extracted with ether. The combined organic extracts were washed further with water and brine, dried over Na2SO4, filtered and the filtrate concentrated in vacuo. Purification of the crude product by way of flash chromatography (SiO2, Hex→1:1 (v/v) Hex:EtOAc) afforded the title compound as a golden yellow oil.
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