Crotonaldehyde reaction with benzaldehyde

Other aldehydes which have been used in the reaction are pro-panal, butanal, glycolaldehyde, 3-hydroxybutanal, and a number of phenylacetaldehydeand benzaldehyde derivatives. Whereas condensation of tryptophan with acetaldehyde takes place even at room temperature and pH 6.7, the reactions with chloral, chloroacetaldehyde, and crotonaldehyde fail entirely. 

Transition-metal mediated carbene transfer from 205 to benzaldehyde generates carbonyl ylides 211 which are transformed into oxiranes 216 by 1,3-cyclization, into tetrahydrofurans 212, 213 or dihydrofurans 214 by [3 + 2] cycloaddition with electron-deficient alkenes or alkynes, and 1,3-dioxolanes 215 by [3 + 2] cycloaddition with excess carbonyl compound120 (equation 67). Related carbonyl ylide reactions have been performed with crotonaldehyde, acetone and cyclohexanone (equation 68). However, the ylide generated from cyclohexanone could not be trapped with dimethyl fumarate. Rather, the enol ether 217, probably formed by 1,4-proton shift in the ylide intermediate, was isolated in low yield120. In this respect, the carbene transfer reaction with 205 is not different from that with ethyl diazoacetate121, whereas a close analogy to diazomalonates is observed for the other carbonyl ylide reactions. 

Aldolization of a,p-unsaturated carbonyl compounds (20) with benzaldehydes in the presence of ATPH is shown in Scheme 6.20. Thus, sequential treatment of a toluene solution of ATPH (3.3 equivalent) with methyl 3-methyl-2-butanoate (20a) (2.0 equivalent) and benzaldehyde (1.0 equivalent) at —78 °C was followed by deprotonation with a THF solution of LTMP (2.3 equivalent). After 30 minutes at the same temperature, a mixture of y-aldol products (21a) and (22a) was obtained in 91% isolated yield with preferential formation of Z isomer (22a) ( -(21a) Z-(21a) = 1 13). In sharp contrast, mesityloxide (20b), senecialdehyde (20c) and the disubstituted a,p-unsaturated carbonyl compounds, methyl crotonate (20d), (T)-3-penten-2-one (20e) and crotonaldehyde (20f) provided the (T)-y-adducts (21b-f), exclusively. The opposite stereoselectivity of the aldol adduct in the reaction of (20a) versus (20b) and (20c) can be explained by the preferable conformation of the extended lithium dienolates confirmed by NMR studies. That is, reaction of ATPH complex of the ester (20a) provided s-cis conformer of the dienolate predominantly, whereas the corresponding dienolates from the ketone (20b) and aldehyde (20c) were found to have s-trans structure. In the cases of the disubstituted substrates (20d-f),... 

The tandem carbonyl ylide/cycloaddition reaction is also observed when crotonaldehyde or acetone is used instead of benzaldehyde (dimethyl fumarate as dipolarophile), whereas with cyclohexanone, an enol ether derived from the carbonyl ylide is isolated [19] (Scheme 9). 

Carbonyl compounds are probably present at low levels in all air samples (Fung and Grosjean, 1981). A great variety of combustion processes produce aldehydes they are particularly abundant in wood smoke, and have also been identified in the products of combustion of natural gas and fuel oil, and in engine exhaust samples. It is likely that they are relatively long-lived intermediates in atmospheric photooxidation reactions. Formaldehyde (CH2O), for example, is always an obligatory intermediate in the conversion of methane to CO2. In nearly all air samples so far examined, formaldehyde has been the most abundant aldehyde, with acetaldehyde, pro-pionaldehyde, acrolein, benzaldehyde, crotonaldehyde, and furfural sometimes present at much lower concentrations (Kuwata et al., 1979 Penkett, 1982 Zhou and... 

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