Abstract
α,β-Ethyl thioacrylate was difuctionalized by a tandem X-C/C=C bond formation reaction. The new system uses Ti (IV) halide as both the Lewis acidic promoter and the halogen source for the Michael-type addition onto the thioacrylate. The titanium enolate species resulting from Michael-type addition react with aldehydes followed by dehydration to afford trisubstituted olefin products. Complete geometric selectivity (>95%) and up to 72% yield have been obtained for 7 examples.
Highlights
The Baylis-Hillman-type C(sp3)-C(sp2) single bond formation has become an active area in synthetic organic chemistry [1,3], but the direct carbon-carbon double formation under Baylis-Hillman-type conditions to give α-halomethyl vinyl carbonyl compounds have not been well documented
We found that α,β-unsaturated ethyl thioacrylate can be functionalized to afford α-halomethyl β-substituted vinyl thioesters under modified conditions
The increased ratio of TiCl4 to (n-Bu)4NI (TiCl4/(n-Bu)4NI = 4/1) was proven to be necessary for the reaction, relatively low yields were obtained for most cases at this stage as shown in Table 1, for which the relatively more complex and stable intermediates generated from the new thioester substrate are responsible
Summary
The Baylis-Hillman-type C(sp3)-C(sp2) single bond formation has become an active area in synthetic organic chemistry [1,3], but the direct carbon-carbon double formation under Baylis-Hillman-type conditions to give α-halomethyl vinyl carbonyl compounds have not been well documented. The reaction was mediated in a highly stereoselective manner by a non-stoichiometric amount of titanium (IV) halides or a mixture of TiCl4/(n-Bu)4NI (and/or TiBr4/(nBu)4NI) (Scheme 1). The new one-pot and three-component reaction was performed by mixing the aldehyde, α,βunsaturated thioester and TiCl4/(n-Bu)4NI in dichloromethane solution at room temperature followed by heating to reflux for 24 hours. The increased ratio of TiCl4 to (n-Bu)4NI (TiCl4/(n-Bu)4NI = 4/1) was proven to be necessary for the reaction, relatively low yields were obtained for most cases at this stage as shown, for which the relatively more complex and stable intermediates generated from the new thioester substrate are responsible.
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