Elimination carbonyl groups

By treatment of an amide with sodium hypobromite or sodium hypochlorite solution (or with the halogen and alkali), the amine of one less carbon atom is produced, the net result being the elimination of the carbonyl group. An example is ... 

Olefin synthesis starts usually from carbonyl compounds and carbanions with relatively electropositive, redox-active substituents mostly containing phosphorus, sulfur, or silicon. The carbanions add to the carbonyl group and the oxy anion attacks the oxidizable atom Y in-tramolecularly. The oxide Y—O" is then eliminated and a new C—C bond is formed. Such reactions take place because the formation of a Y—0 bond is thermodynamically favored and because Y is able to expand its coordination sphere and to raise its oxidation number. 

The phosphorus ylides of the Wittig reaction can be replaced by trimethylsilylmethyl-carbanions (Peterson reaction). These silylated carbanions add to carbonyl groups and can easily be eliminated with base to give olefins. The only by-products are volatile silanols. They are more easily removed than the phosphine oxides or phosphates of the more conventional Wittig or Homer reactions (D.J. Peterson, 1968). 

The 4-Hydroxy-thiazoles are characterized by infrared absorption near 1610 cm (KBr) (3) or 1620 to 16.S0cm (CCI4) (8), indicating a strongly polarized carbonyl group. H-5 resonates near 5.6 ppm in the NMR spectrum like similar protons in other mesoionic compounds (3). Two fragmentations of the molecular ion are observed in the mass spectra. The first involves rupture of the 1,2 and 3,4 bonds with loss of C2R 0S . In the second, the 1,5 and 3,4 bonds are cleaved with elimination of C2R 0. ... 

A number of compounds of the general type H2NZ react with aldehydes and ketones m a manner analogous to that of primary amines The carbonyl group (C=0) IS converted to C=NZ and a molecule of water is formed Table 17 4 presents exam pies of some of these reactions The mechanism by which each proceeds is similar to the nucleophilic addition-elimination mechanism described for the reaction of primary amines with aldehydes and ketones... 

Elimination from the tetrahedral intermediate to restore the carbonyl group... 

Lactones, l xictides, iMciams, and Lactims. When the hydroxy acid from which water may be considered to have been eliminated has a trivial name, the lactone is designated by substituting -olactone for -ic acid. Locants for a carbonyl group are numbered as low as possible, even before that of a hydroxyl group. 

Formation and Elimination of Multiple Bond Functionalities. Reactions that involve the formation and elimination of multiple bond functional groups may significantly effect the color of residual lignin in bleached and unbleached pulps. The ethylenic and carbonyl groups conjugated with phenoHc or quinoid stmctures are possible components of chromophore or leucochromophore systems that contribute to the color of lignin. 

Some cleavage takes place even if the phenoHc hydroxyl is blocked as an ether link to another phenylpropane unit and quinonemethide formation is prevented. If the a- or y-carbon hydroxyl is free, alkaH-catalyzed neighboring-group attack can take place with epoxide formation and P-aryloxide elimination. In other reactions, blocked phenoHc units are degraded if an a-carbonyl group is present. 

Mechanism of the initial reaction, known as alkaline peeling, is shown in equation 4. EnoHzations and tautomerizations take place easily because of the contiguous hydroxyl groups. The hydroxyl or substituted hydroxyl on the second, ie, P-carbon, from a carbonyl group is released from the molecule by P-elimination. 

It should be noted that when 3-acylisoxazoles (116) are heated with a base such as sodium ethoxide, the acyl group is eliminated to give a carboxylate salt and a /3-ketonitrile (117). The reaction probably occurs via initial attack at the carbonyl group (46G206). 

Three-dimensional potential energy diagrams of the type discussed in connection with the variable E2 transition state theory for elimination reactions can be used to consider structural effects on the reactivity of carbonyl compounds and the tetrahedral intermediates involved in carbonyl-group reactions. Many of these reactions involve the formation or breaking of two separate bonds. This is the case in the first stage of acetal hydrolysis, which involves both a proton transfer and breaking of a C—O bond. The overall reaction might take place in several ways. There are two mechanistic extremes ... 

Dinitrophenylhydrazine reacts with carbonyl groups with the elimination of water to yield hydrazones (I) and with aldoses or ketoses to yield colored osazones (II). 

A recent modification of this technique utilizes A,A-d2-propylamine as the solvent for the lithium reduction, thereby eliminating the inconveniences associated with the preparation and handling of liquid deuterioammonia. Under these conditions the reaction can be carried out at room temperature and less overreduction of the carbonyl group is observed. For example, the reduction of A" -3-keto steroids (159) under these conditions, followed by back exchange in protic media, leads to the corresponding 5a-di-3-ketones (160) which exhibit good isotopic purity. ... 

Thioketals are readily formed by acid-catalyzed reaction with ethane-dithiol. Selective thioketal formation is achieved at C-3 in the presence of a 6-ketone by carrying out the boron trifluoride catalyzed reaction in diluted medium. Selective protection of the 3-carbonyl group as a thioketal has been effected in high yield with A" -3,17-diketones, A" -3,20-diketones and A" -3,l 1,17-triones in acetic acid at room temperature in the presence of p-toluenesulfonic acid. In the case of thioketals the double bond remains in the 4,5-position. This result is attributed to the greater nucleophilicity of sulfur as compared to oxygen, which promotes closure of intermediate (66) to the protonated cyclic mercaptal (67) rather than elimination to the 3,5-diene [cf. ketal (70) via intermediates (68) and (69)]." " ... 

As one might expect, most of the reported cases of Camps quinoline syntheses involve reactions in which only one of the carbonyl groups is enolizable, thus eliminating the regioselectivity problem. 

If mutarotation were not a factor, the threo pair would give the isomer having the phenyl group and nitrogen atom in a cis relationship and the erythro pair the isomer with the phenyl and carbonyl groups cis. Since it is doubtful, at least in some cases, that steric integrity is maintained in acetic anhydride prior to elimination, the subsequent... 

In an alternative reaction course, the primary amino group reacts with C-3, while the intermediate 134 undergoes cyclization either via nucleophilic attack by a Y function at the C-1 atom followed by elimination of HXR (also formed due to possible hydrolysis of the initial products and intermediates) or with involvement of one of the carbonyl groups (intermediates 132 and 136) (81UK1252 91UK103). 

In the case of the cyclohexane derivative 7 however, that bears an equatorial acetate group, two axial cis-/3-hydrogens are available, and elimination in both directions is possible. The pyrolysis of 7 yields the two elimination products 8 and 6. Formation of product 8 is strongly favored, because the new double bond is in conjugation to the ester carbonyl group. ... 

Condensation of piperazine with 2-methoxytropone gives the addition-elimination product 12 [2]. Alkylation of the remaining secondary amino group with bromoketone 13, itself the product from acylation of dimethyl catechol, gives aminoketone 14. Reduction of the carbonyl group with sodium borohydride leads to secondaiy alcohols 15 and 16. Resolution of these two enantiomers was achieved by recrystallization of their tartrate salts to give ciladopa (16) [3],... 

All of these ehimnddon reacdons contain fi-carbonyl groups in the nltro compounds Of course, masked carbonyl groups are also frequently employed for such fi-elimination of HNO, as shown in Eq 7131, Eq 7 133, and Eq 7 133In these cases, the sulfinylmethyl or hydroxymethyl group is converted into the carbonyl group by the Pummerer rearrangement or by simple oxidation... 

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