1.3- diketones nitrostyrenes

Nitroalkenes, e.g. 1 -nitrocyclohexene, 1-nitrocycloheptene, 1-nitrocyclooctene and (3-methyl-j8-nitrostyrene, undergo Michael addition with the enolate anions of (3-ketoesters. The resulting acids undergo a Nef reaction to give 1,4-diketones, which yield furans by subsequent ring closure (Scheme 18) (59LA(626)7l). 

Remarkably, the reaction also tolerated the use of differently substituted a-alkyl-p-ketoesters as Michael donors, leading to the formation of compounds containing two contiguous stereogenic centers, one of them a quaternary one, in good diastereo- and enantioselectivities (Scheme 4.6). Masked cyclic 1,3-diketones such as 2-hydroxy-1,4-naphthoquinols have also been successfully applied in this context also showing the extraordinary performance of catalyst 68a in terms of both yields and enantioselectivities. There is also one example of a vinylogous Michael reaction between a,a-disubstituted dicyanoacrylates and nitroalkenes for which Takemoto s catalyst has also been identified as the most efficient promoter of the reaction. Moreover a solid-supported version of this catalyst has also been developed by Takemoto himself and tested in the reaction of diethylmalonate with nitrostyrene with success. ... 

In the domino Michael/alkylation reaction applied to the synthesis of 3-(2H)-furanones, the ethyl 4-bromoacetoacetate 203 and nitrostyrene 204 were first trialed with a range of catalysts. In this instance, the so-called modified Feist Binary reaction was completed with an I-threonine bifunctional tertiary amine/thiourea catalyst 205 to produce the furanone 206 in excellent yield and high enantioselec-tivity (Scheme 7.42) [107]. In another report, the furan ring as part of other bicyclic or tricyclic systems was also prepared through an enantioselective Michael addi-tion/nucleophilic substitution reaction (Scheme 7.43) [108]. When diketones and ( )-P,P-bromonitrostyrenes 207 were stirred, again with a bifunctional thiourea... 

Meanwhile, Rueping and eoworkers reported a sustainable protocol for the enantioselective domino reaetion of cyclohexa-l,2-dione with a variety of substituted p-nitrostyrenes giving access for the first time to eomplex, polyfunctionalised hieyelo[3.2.1]oetan-8-ones. Utilising Cinchona derivative 25 in just 1-2 mol% loading, while maintaining a diketone-nitro-olefin ratio... 

Organocatalytic asymmetric Michael reactions were first performed in IL media by Toma and coworkers [35]. Carbonyl or 1,3-dicarbonyl compounds reacted with P-nitrostyrene or 2-(P-nitrovinyl)thiophene in [bmim][PF6] in the presence of proline to afford corresponding Michael adducts 7 in moderate to high yields and in some cases with rather high syn-diastereoselectivities (Scheme 22.4). The enantioselectivity of the processes, however, was poor (<60% ee). 1,3-Diketones appeared less active donors than ketones and especially than aldehydes in the IL medium. 

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