A, 3-Unsaturaled aldehydes

The methyl enol ether 37 is oxidized to the a,/3-unsaturated aldehyde 39 via hemiacetal 38. Unsaturated aldehyde 39, elongated one carbon from the aldehyde 36, is prepared by the Wittig reaction of 36 to give 37, and application of this reaction[ 88]. 

Ailyl enol carbonates derived from ketones and aldehydes undergo Pd-cat-alyzed decarboxylation-elimination, and are used for the preparation of a, /3-unsaturated ketones and aldehydes. The reaction is regiospecific. The regio-isomenc enol carbonates 724 and 726, prepared from 723, are converted into two isomeric enones, 725 and 727. selectively. The saturated aldehyde 728 can be converted into the a,/3-unsaturated aldehyde 730 via the enol carbonate 729[459]. 

Diaryl disulfides and diselenides add to alkynes to afford the (Z)-l, 2-bis(ar-ylthio)alkenes 193 and (Z)-l,2-bis(arylseleno)alkenes 194. Under CO pressure, carbonylative addition takes place to give thio esters and the selenoketones 195[I07], The selenoketones are converted into the /J-seleno-a, 3-unsaturated aldehydes 196 by Pd-catalyzed hydrogenolysis with HSnBu3[108,109],... 

Reaction of triethylsilane with a, /3-unsaturated aldehydes catalyzed by Pd on carbon gives a /raff5-l,4-adduct as the main product. Reaction of acrolein gave the adduct in 86% yield, in which the 1,4-adduct 48 was 97% and the 1,2-adduct was 3%[44]. 

P carbon atom of an a 3 unsatu rated carbonyl compound is elec trophilic nucleophiles especially weakly basic ones yield the prod ucts of conjugate addition to a 3 unsaturated aldehydes and ketones... 

The simplest a 3 unsaturated aldehyde acrolein is prepared by heating glycerol with an acid catalyst Suggest a mechanism for this reaction... 

Chloro-a,/3-unsaturated aldehydes condense with ammonium thiocyanate to give isothiazoles (76EGP122249). 2,3-Diphenylcyclopropenone reacts with iV-sulfinyl-cyclohexylamine in the presence of nickel tetracarbonyl to give the isothiazolin-3-one 1-oxide (197) (79SST(5)345). Cholesteryl acetate reacts with trithiazyl trichloride in pyridine to give the isothiazolo steroid (198) (77JCS(P1)916). 

An oxazolidine was used to protect the carbonyl group in an a,/3-unsaturated aldehyde during reduction of the carbon-carbon double bond by H2/Raney Ni. It... 

Table 11. a-and (3-Fluorinated a, 3-Unsaturated Aldehydes in Olefination Reactions [43 ... 

The p-hydroxy aldehyde products of aldol addition undergo dehydration on heating, to yield a,(3-unsaturated aldehydes ... 

Stabilized anions exhibit a pronounced tendency to undergo conjugate addition to a,p-unsaturated cai bonyl compounds. This reaction, called the Michael reaction, has been described for anions derived from (3-diketones in Section 18.13. The enolates of ethyl acetoacetate and diethyl malonate also undergo Michael addition to the (3-caibon atom of a,(3-unsaturated aldehydes, ketones, and esters. For example. 

A substituted a,/3-unsaturated aldehyde, cinnamaldehyde, has been observed to undergo the same type of two-step 1,3-cycloaddition reaction with a cyclohexanone enamine as acrolein does, forming in this case a stereo-isomeric mixture of substituted bicycloaminoketones in excellent yield (29a,31a,31b). 

Skraup proposed a simple mechanism involving imine formation followed by an acid-mediated cyclization. Unfortunately the observed regioselectivity is not consistent with the proposed mechanism when, for example, electron-rich aniline 4 reacts with a, 3-unsaturated aldehyde 5 to give quinoline 6. ... 

A variety of oxidants have been used in the Skraup/Doebner-von Miller reaction between anilines and a, 3-unsaturated aldehydes. For example, aniline 23 was reacted... 

Various competitive reactions can reduce the yield of the desired Michael-addition product. An important side-reaction is the 1,2-addition of the enolate to the C=0 double bond (see aldol reaction, Knoevenagel reaction), especially with a ,/3-unsaturated aldehydes, the 1,2-addition product may be formed preferentially, rather than the 1,4-addition product. Generally the 1,2-addition is a kinetically favored and reversible process. At higher temperatures, the thermodynamically favored 1,4-addition products are obtained. 

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