Practical Synthesis of Linear α-Iodo/Bromo-α,β-unsaturated Aldehydes/Ketones from Propargylic Alcohols via Au/Mo Bimetallic Catalysis
Longwu Ye and Liming Zhang*
*Department of Chemistry & Biochemistry, University of
California, Santa Barbara, CA 93106-9510, Email: zhang
chem.ucsb.edu
L. Ye, L. Zhang, Org. Lett., 2009, 11, 3646-3649.
DOI: 10.1021/ol901346k
see article for more reactions
Abstract
An efficient synthesis of α-iodo/bromo-α,β-unsaturated aldehydes/ketones directly from propargylic alcohols is catalyzed collaboratively by Ph3PAuNTf2 and MoO2(acac)2, and Ph3PO as an additive helps suppress undesired enone/enal formation. Notable features of this method include low catalyst loadings, mild reaction conditions, and mostly good diastereoselectivity.
see article for more examples
General procedure for the preparation of α-iodoenones
Ph3PO (4.2 mg, 0.015 mmol), MoO2(acac)2 (1.0 mg, 0.003 mmol), Au(PPh2)NTf2 (2.2 mg, 0.003 mmol), and NIS (81 mg, 0.36 mmol) were added sequentially to a solution of the propargyl alcohol (0.30 mmol) in anhydrous CH2Cl2 (6.0 mL, 0.05 M) at room temperature. The reaction was stirred for three hours before quenched with saturated aqueous sodium bisulfite. The mixture was extracted with Et2O (3 x 8 mL). The combined organic phases were washed with H2O (10 mL) and brine (10 mL), dried with anhydrous MgSO4, and filtered. The filtrate was concentrated, and the residue was purified through silica gel flash column chromatography (hexanes/ethyl acetate = 50/1) to yield the desired α-iodo-α,β-unsaturated carbonyl compounds.
General procedure for the preparation of α-bromoenones
Ph3PO (8.4 mg, 0.03 mmol), MoO2(acac)2 (2.0 mg, 0.006 mmol), Au(PPh3)NTf2 (4.4 mg, 0.006 mmol), and NBS (64 mg, 0.36 mmol) were added sequentially to a solution of the propargyl alcohol (0.30 mmol) in anhydrous CH2Cl2 (6.0 mL, 0.05 M) at room temperature. The reaction was stirred for seven hours before quenched with saturated aqueous sodium bisulfite. The mixture was extracted with Et2O (3 x 8 mL). The combined organic phases were washed with H2O (10 mL) and brine (10 mL), dried with anhydrous MgSO4, and filtered. The filtrate was concentrated, and the residue was purified through silica gel flash column chromatography (hexanes/ethyl acetate = 50/1) to yield the desired α-bromo-α,β-unsaturated carbonyl compounds.
Gold-Catalyzed Efficient Preparation of Linear α-Iodoenones from Propargylic Acetates
M. Yu, G. Zhang, L. Zhang, Org. Lett., 2007, 9, 2087-2090.
Key Words
Iodination, Bromination, NIS, NBS, Enones, Alkenyl Halides
ID: J54-Y2009-2500
