Abstract
In the Baylis-Hillman reaction of aryl aldehydes with phenyl vinyl ketone we have observed exclusive formation of diadducts 4, and that the yields of diadduct can reach 80% with increasing amounts of phenyl vinyl ketone. On the other hand, for phenyl acrylate and phenyl thioacrylate, only the normal Baylis-Hillman adduct was obtained. The effects of substituents were also examined and a plausible reaction mechanism is proposed for the formation of compounds 4.
Highlights
Great progress has been made in the implementation of the Baylis-Hillman reaction [1], since Baylis and Hillman first reported in 1972 the reaction of acetaldehyde with ethyl acrylate and acrylonitrile in the presence of catalytic amounts of 1,4-diazabicyclo[2,2,2]octane (DABCO) [2], and even a catalytic asymmetric version has been published [3]
Molecules 2002, 7 example, using p-nitrobenzaldehyde (1.0 eq) and methyl vinyl ketone (MVK) (2.0 eq) as substrates in the presence of catalytic amounts of DABCO (0.1 eq) in DMSO or DMF, we found that, besides the normal BaylisHillman reaction product 1a, compound 2a was formed at the same time as a 2:3 mixture of synand anti-isomers [5] (Scheme 1) and the substituent effects of aryl aldehydes were examined in detail [5]
In the reaction of p-nitrobenzaldehyde (1.0 eq.) with phenyl vinyl ketone (PVK) (1.0 eq.) in the presence of DABCO (10 mol-%) in DMF, the corresponding Baylis-Hillman adduct 3a was not formed at all
Summary
Great progress has been made in the implementation of the Baylis-Hillman reaction [1], since Baylis and Hillman first reported in 1972 the reaction of acetaldehyde with ethyl acrylate and acrylonitrile in the presence of catalytic amounts of 1,4-diazabicyclo[2,2,2]octane (DABCO) [2], and even a catalytic asymmetric version has been published [3]. Molecules 2002, 7 example, using p-nitrobenzaldehyde (1.0 eq) and MVK (2.0 eq) as substrates in the presence of catalytic amounts of DABCO (0.1 eq) in DMSO or DMF, we found that, besides the normal BaylisHillman reaction product 1a, compound 2a was formed at the same time as a 2:3 mixture of synand anti-isomers [5] (Scheme 1) and the substituent effects of aryl aldehydes were examined in detail [5] This interesting result stimulated us to further examine the influence of the R group of the BaylisHillman acceptor [C=C-C(O)R] on this reaction. We synthesized phenyl vinyl ketone (PVK) [6], phenyl acrylate [7], and phenyl thioacrylate [8] as the Baylis-Hillman acceptors and carefully examined the reaction products formed under the traditional Baylis-Hillman reaction conditions
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