Unsaturated aldehydes conjugated

Analogous to conjugated unsaturated aldehydes, conjugated unsatur-ted ketones react after the above scheme to saturated ketones [35] (table 17). 

Ethynyl carbinols rearrange to conjugated unsaturated aldehydes. Copper or silver salts cataly2e isomeri2ation of the acetate to an aHenic acetate, which can be hydroly2ed to an unsaturated aldehyde (204). 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

Unimolecular, 373 Unsaturated, 174 Unsaturated aldehyde, conjugate addition reactions of,... 

In basic aqueous solutions with a [Rh(COD)2]BF4 catalyst, phenyltin trichloride was found to react with aromatic aldehydes or unsaturated ketones. In the presence of a strong aqueous alkali (KOH) PhSnCU is readily hydrolysed and the products of this reaction, such as e.g. PhSn(OH)3 add to the carbonyl function of aldehydes or undergo conjugate addition to unsaturated ketones (Scheme 6.35). In the absence of KOH no reaction takes place at all. Yields are generally high [73]. 

Complex hydrides can be used for the selective reduction of the carbonyl group although some of them, especially lithium aluminum hydride, may reduce the a, -conjugated double bond as well. Crotonaldehyde was converted to crotyl alcohol by reduction with lithium aluminum hydride [55], magnesium aluminum hydride [577], lithium borohydride [750], sodium boro-hydride [751], sodium trimethoxyborohydride [99], diphenylstarmane [114] and 9-borabicyclo[3,3,l]nonane [764]. A dependable way to convert a, -un-saturated aldehydes to unsaturated alcohols is the Meerwein-Ponndorf reduction [765]. 

Reduction of unsaturated aromatic aldehydes to unsaturated hydrocarbons poses a serious problem, especially if the double bond is conjugated with the benzene ring or the carbonyl or both. In Clemmensen reduction the a,)8-unsaturated double bond is usually reduced [160], and in Wolff-Kizhner reduction a cyclopropane derivative may be formed as a result of decomposition of pyrazolines formed by intramolecular addition of the intermediate hydrazones across the double bonds [280]. The only way of converting unsaturated aromatic aldehydes to unsaturated hydrocarbons is the reaction of... 

The first step is a condensation of the aldol type (see Section 5.18.2, p. 799) involving the nucleophilic addition of the carbanion derived from the methyl ketone to the carbonyl-carbon of the aromatic aldehyde. Dehydration of the hydroxyketone to form the conjugated unsaturated carbonyl compound occurs spontaneously. 

Conjugated unsaturated aldehydes (e.g., cltral, g,g-dimethyl-acrolein ). ... 

Intramolecular hydrogen-transfer to a nearby free-radical is a general phenomenon (see Chapter 10) and in a diradical (13) can, in principle, occur in either of the two ways depicted, to give either (a) a non-conjugated unsaturated aldehyde (14), or (b) a ketene (15). In the C-nor-ketone 12) hydrogen transfer... 

The 1,2-hydrogen shift on the propargyl carbon concomitant with elimination of the proton from the hydroxyl group generates a vinylruthenium species G, which probably undergoes protonolysis to yield the conjugated aldehyde and unsaturated cationic ruthenium complex H. 

Yadav, J. S., Anuradha, K., Reddy, B. V. S., Eeshwaraiah, B. Microwave-accelerated conjugate addition of aldehydes to -unsaturated ketones. Tetrahedron Lett. 2003, 44, 8959-8962. 

Knoevenagel reaction A condensation reaction in which a methylene unit that has two adjacent -M groups such as carbonyl, ester or nitro groups, reacts in the presence of base with an aldehyde or ketone, that usually does not have an a-hydrogen. Dehydration usually follows to yield the conjugated unsaturated compound. 

Reduction of conjugated unsaturated aldehydes or ketones is sometimes accompanied by a shift in the position of the double bond (7.110). In other cases pyrazoline derivatives may be formed these decompose yielding cyclopropanes isomeric with the expected alkene (7.111). 

So far we have shown you conjugate additions mainly of a,P-unsaturated aldehydes and unsaturated a,P-ketones. You won t be at all surprised to learn, however, that unsaturated acids, esters, amides, and nitriles—in fact all carboxylic acid derivatives—can also take part in conjugate addition reactions. Two examples, an amide and an ester, are shown on the right below. But notice how the selectivity of these reactions depends on the structure of the unsaturated compound compare the way butyllithium adds to this a,P-unsaturated aldehyde and a,P-unsaturated amide. Both additions are irreversible, and BuLi attacks the reactive carbonyl group of the aldehyde, but prefers conjugate addition to the less reactive amide. Similarly, ammonia reacts with this acyl chloride to give an amide product that derives from direct... 

A feature of the heated palladium system is that it is catalytically active in proportion to its hydrogen permeability, so reducible compounds will be completely hydrogenated on passing through hydrogenation proved to be specific to compounds with conjugated unsaturated bonds such as dienes, a,/3-unsaturated aldehydes, ketones and nitriles, but did not occur otherwise. 

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