Unsaturated systems aldehydes

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

Michael addition of aromatic or heterocyclic aldehydes (via cyanohydrins) to o. unsaturated systems. Also addilion of aliphatic aldehydes catalyzed by thiazoFium yKds... 

From the foregoing discussion, it is clear that DPM rearrangements are very general for a variety of 1,4-unsaturated systems, such as, 1,4-dienes, (3,7-unsaturated aldehydes and ketones, and different 1-aza-1,4-diene derivatives. Surprisingly, the literature was devoid of studies describing the photoreactivity of the closely related 2-aza-1,4-diene derivatives. For many years, the only studies in this area were carried out by Mariano and his co-workers [60] on the photochemistry of iminium salts derived from 2-aza-1,4-dienes. The results obtained demonstrated the synthetic utility of the photocyclizations of iminium salts to different heterocycles, in reactions that are initiated by intramolecular single electron transfer [60]. 

The acyclic precursor is an oc, 3-unsaturated amido aldehyde that was condensed with iV-methylhydroxylamine to generate the nitrone ( )-48, which then underwent a spontaneous cycloaddition with the alkene to afford the 5,5-ring system of the isoxazolidinyl lactam 47. The observed product arises via the ( )-nitrone transition state A [or the (Z)-nitrone equivalent] in which the position of the benzyl group ot to the nitrone effectively controls the two adjacent stereocenters while a third stereocenter is predicted from the alkene geometry. Both transition states maintain the benzyl auxiliary in an equatorial position and thus avoid the unfavorable 1,3-diaxial interaction with the nitrone methyl or oxygen found in transition state B. Semiempirical PM3 calculations confirm the extra stability, predicting exclusive formation of the observed product 47. Related cycloadducts from the intramolecular reaction of nitrones containing ester- rather than amide-tethered alkene functionality are also known (83-85). 

Whereas additions of carbon radicals to alkene moieties are the best characterized homolytic additions, carbon radicals are known to add to a wide range of unsaturated systems. These include polyenes, alkynes, arenes, heteroarenes, carbon monoxide,isonitriles, °° ° nitriles, ° imines and derivatives, ° ° aldehydes,nitrones, and thiones. ° Many of these reactions, such as addition of an alkyl radical to a carbonyl group, ° are thermodynamically unfavorable and readily reversible, and they form the basis of composite group-transfer reactions discussed below. 

The chemistry of imidates and their methods of synthesis have been reviewed [32], Imidates are mainly available via the Pinner synthesis, via iminochlorides, from amides, from aldehydes and ketones, and via unsaturated systems [32]. 

One possible mechanism for the degradation of 2,4-decadienal is the retro-aldol mechanism proposed by Josephson and Lindsay (8) for the oxidation of a,B-unsaturated fatty aldehydes. In their investigation of the degradation products of 2,4-decadienal, Josephson and Lindsay (9) identified 2-octenal and hexanal as primary products. Both 2-octenal and hexanal were identified in the present systems. 

The effectiveness of the 1,1.1-trichlorotrifluoroethane/triphenylphosphane system in reactions with aldehydes, which lead to the formation of (trifluoromethyl)alkenes, has been demonstrated. The reaction with aromatic and a,) -unsaturated aliphatic aldehydes proceeds with high stereoselectivity (the Z-isomcr is formed exclusively), whereas the reaction with other aliphatic aldehydes affords a mixture of the Z- and /T-isomers in proportions ranging from 2 1 to 3 1. 

Besides the Michael addition of heteroatomic nucleophiles initiating cyclocondensations, acceptor substituted unsaturated systems can also be reacted with carbon nucleophiles stemming from aldehydes in the sense of an umpolung, generally referred to as the Stetter reaction [244-246]. This process is organocatalytic and furnishes in turn 1,4-dicarbonyl compounds, intermediates that are well suited for Paal-Knorr cyclocondensations giving rise to furans or pyrroles. Among numerous heterocycles furans and pyrroles have always been the most prominent ones since they constitute important classes of natural products [247-249], of synthetic... 

Organozinc addition reactions to unsaturated systems lead to an intermediate zinc compound which is in most cases further hydrolyzed to give the corresponding protonated organic compound. This intermediate can also be trapped by reaction with electrophiles (see Electrophile) (E+) such as aldehydes, acyl chlorides, organic halides, silyl halides, and so on. Depending on the nature of the electrophile (see... 

Although Smh is more chemoselective than traditional dissolving metal reagents, it does react with sulfoxides, epoxides, the conjugated double bonds of unsaturated ketones, aldehydes and esters, alkyl bromides, iodides and p-toluenesulfonates. It does not, however, reduce carboxylic acids, esters, phosphine oxides or alkyl chlorides. In common with most dissolving metal systems, ketones with an a-hetero substituent suffer loss of the substituent rather than reduction of the carbonyl group. ... 

Lewis acids prefer to lie syn to the smaller substituent of the carbonyl, e.g. syn to H for aldehydes, anti to —OR for simple alkyl esters. In a, 3-unsaturated systems, Lewis acid coo ination syn to the double bond favors the s-trans conformation, but in two crystal structures, where coordination anti to the alkene occurs, s-cis complexes are observed. - " Finally, chelation with titanium and tin occurs readily and yields stable, crystalline complexes. 

This chapter concerns the net conversion of a C =X ir-bond (X = O and N) to various three-membered ring heterocycles. The most common such process is the conversion of an aldehyde or ketone to a homologous epoxide. These reactions will be discussed along with the analogous process which takes place on imines and related compounds. Additionally, methods to effect the addition of elements other than carbon across either unsaturated system will considered. The synthesis of thiiranes by the addition of carbon across the C—S rr-bond is the subject of a recent comprehensive review and will not be covered here. 

The Criegee mechanism 13-15, 17) for ozonolysis has been of tremendous importance in giving a better understanding of the course of the ozonolysis reaction—in particular, the nature and fate of the active oxygen-containing ozonolysis products. It leaves in doubt, however, the nature of the initial attack of ozone on an unsaturated system and of the intermediates leading to the formation of the primary cleavage products, the zwitterion (IV) and the aldehyde or ketone (V). 

Cyclopropanation of a,jS-unsaturated AT-methoxy-AT-methylamides 5 with dimethyloxo-sulfonium methanide afforded the cyclopropanecarboxamides 6 in yields far superior to those obtained with the corresponding a,/J-unsaturated ketones. In almost all cases, the trans-isomer was exclusively obtained in analogy to the cyclopropanation of the corresponding unsaturated ketones. The oxygen atom of the methoxy group on the A -methoxy-A -methyl-amide 5 was found to facilitate the reaction. The substituted amides 6 can be converted to ketones (methylmagnesium bromide), aldehydes (diisobutylaluminum hydride) and carboxylic acids (potassium rerf-butoxide/water). It is noteworthy that cyclopropanecarbaldehydes and -carboxylic acids, which are not directly accessible from the corresponding a,)8-unsaturated systems under standard cyclopropanation reactions, can be obtained indirectly by this method. 

The unsaturated Cg aldehydes and alcohols probably arise in wheat from cleavage of the 9—10 double bond of unsaturated C g fatty acids, linoleic and linolenic acids (Figure 2). Galliard and coworkers (12,13) have partially purified enzyme systems capable of catalyzing these transformations. Lipoxygenase initially converts linoleic and linolenic acids to 9-hydroperoxides which are subsequently cleaved by hydroperoxide lyase to volatile Cg unsaturated aldehydes and 9-oxo-nonanoic acid. The 3-enals are the primary volatile cleavage products from the fatty acids and these are transformed by an isomerase to the more stable 2—enals (14). The 3—enals are rather unstable but Hatanaka et al. (15) have confirmed their presence in plant tissue with authentic samples. The Cg... 

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