Abstract
E -α,β-Unsaturated ketones can be obtained with complete E -selectivity by a sequential reaction of dichloroketones with a variety of aldehydes.
This transformation was promoted by SmI2 , SmI2 in the presence of FeCl3 or CrCl2 . The best results were obtained when CrCl2 was used as the metallating agent. A mechanism based on a successive aldol-type reaction
and a β-elimination is proposed to explain these results.
Key words
alkenes - chromium - diastereoselectivity - samarium - ketones - sequential reactions
References and Notes
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General Procedure for the Synthesis of Compounds 3
SmI2 (3 mmol, 6 equiv) in THF (30 mL), or CrCl2 (3 mmol, 6 equiv) in THF (13 mL), was added to a stirred solution of 1,1-dichloroketone
(0.5 mmol, 1 equiv) and the correspond-ing aldehyde (0.5 mmol, 1 equiv) in THF (2
mL) under nitrogen atmosphere. The reaction was refluxed for 2 h, and then the reaction
was quenched by the addition of 1.0 M aq HCl. Standard workup afforded the crude α,β-enones
3 which were purified by flash column chromatography on silica gel (hexane-EtOAc, 10:1),
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