[CH:1]([C:3]1[S:7][CH:6]=[C:5](B(O)O)[CH:4]=1)=[O:2].[N:11]([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])=[N:12][C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14]>C1COCC1.C([O-])(=O)C.[Cu+2].C([O-])(=O)C>[CH:1]([C:3]1[S:7][CH:6]=[C:5]([N:11]([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])[NH:12][C:13]([O:15][C:16]([CH3:17])([CH3:18])[CH3:19])=[O:14])[CH:4]=1)=[O:2]To a solution of 5-formylthiophen-3-ylboronic acid (2 g, 12.82 mmol) and di-tert-butyl azodicarboxylate (1.476 g, 6.41 mmol) in THF (12 mL) under nitrogen was added copper(II) acetate (0.116 g, 0.641 mmol) in one portion according to the procedure of T. Uemura and N. Chatani (J. Org. Chem. 2005, 70, 8631-8634). The suspension was then stirred for 18.5 hours at room temperature. The resulting brown solution was then concentrated and the residue was dissolved in DCM and methanol and loaded on silica and applied to a 40M Biotage column. Elution with a gradient of 10 to 20% ethyl acetate in hexanes gave compound 11 (1.888 g, 86%) as a yellow crust. LRMS (ESI): calc. 342.12; found 365.2 (MNa)+.
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