Abstract
A three-component halogeno aldol reaction has been developed by using titanium tetrachloride as the halogen source as well as the Lewis acid mediator. The dehydration and elimination of hydrogen chloride were inhibited by conducting the reaction at 0 °C in dichloromethane or at room temperature with a shortened reaction time. Seven examples were examined, giving good to high yields (61 - 92%) and modest stereoselectivity (syn/anti: 2.2/1.0 - 8.4/1.0).
Highlights
The formation of C(sp3)-C(sp3) bond via aldol reaction represents an important topic in organic chemistry [2,3,4]
This halogeno aldol reaction was achieved by using an excess amount of α,β-unsaturated ketone (2.0 eq) and TiCl4 (1.2 eq) and performed at 0 °C in dichloromethane
Unlike the C=C formation system, the combination of TiCl4/(n-Bu)4NI was proven to be inefficient for the present ketone-based halogeno aldol reaction
Summary
The formation of C(sp3)-C(sp3) bond via aldol reaction represents an important topic in organic chemistry [2,3,4]. It acts as the key step of the Baylis-Hillman reaction [5,6]. When we attempted to extend the reaction scope to the use of α,βunsaturated ketones, we failed to obtain the anticipated Baylis-Hillman adducts or halogeno aldol products under the established conditions [7b]. While the further study of the new C=C bond formation is ongoing in our laboratories, we concurrently made efforts to control the ketone-based system to produce halogeno aldol adducts prior to dehydration. We describe the preliminary results of this method which is represented in Scheme 1c
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