Aldehyde moiety

Acrolein is a highly reactive compound because both the double bond and aldehydic moieties participate in a variety of reactions. 

The rate of aspartame degradation in dry mixes is more dependent on the water activity than on the temperature (23). In dry mixes, aspartame may also engage ia Maillard reactions with the aldehyde moieties of flavoting agents, resulting ia the loss of sweetness and flavor. Use of the corresponding acetals of the flavor compounds to avoid this reaction has been reported (24). 

FIGURE 6.21 Collagen fibers are stabilized and strengthened by Lys-Lys cross-links. Aldehyde moieties formed by lysyl oxidase react in a spontaneous nonenzymatic aldol reaction. 

During indolization of the 3, 6 and 7-quinolylhydrazones, formation of the new C-C bond occurs between the appropriate carbon atom of the ketone/aldehyde moiety and the 4, 5 and 8 carbon atoms of the quinoline nucleus. It is consistent with the mechanism of formation of the C-C bond during indolization and the direction of electrophilic substitution in the quinoline nucleus. °... 

After 19 hours, no reaction between the zinc chelate 2 and benzaldehyde can be detected at 20 °C. However, 10 mol % of the zinc chelate effectively catalyzes theenantioselective addition of diethylzinc to aromatic aldehydes. The predominant formation of the S-configurated products, effected by this conformationally unambiguous catalyst, can be explained by a six-mem-bered cyclic transition state assembly17. The fact that the zinc chelate formed from ligand M is an equally effective catalyst clearly demonstrates that activation of the aldehyde moiety does not occur as a consequence of hydrogen bond formation between the ammonium proton of the pyrrolidine unit and the aldehydic oxygen. 

Miscellaneous Identified Inhibitors. 3-Acetyl-6-methoxy-benzaldehyde is present in the leaves of the desert shrub Encelia farinosa. It is apparently leached from the leaves and washed into the soil by rain. Concentrations of approximately 0.5 mg. per gram of dried leaf material have been measured. In sand culture studies, growth of tomato seedlings was inhibited by 50 p.p.m. while 115 p.p.m. reduced growth by 50% (53). A concentration of 250 p.p.m. killed the test plants within one day. The structure was confirmed by synthesis, and the synthetic material was shown to be as active as the natural product (54). Derivatives were also prepared in which a cyano, nitro, or amino group was substituted for the aldehyde moiety. The amino derivative was reported to be the most highly toxic. 

The relatively basic (hydroxyalkyl)phosphines act toward LMCs as reductants and, compatible with this, also as strong nucleophiles. We have studied such reactions in aqueous and D2O solutions by P-, H-, and C-NMR spectroscopies (including 2D correlation methods), product isolation and, when possible, X-ray analysis of isolated compounds or their derivatives. Thus, aromatic aldehyde moieties present in lignin (e.g., 3) are reduced to the corresponding alcohols (see 4) with co-production of the phosphine oxide in D2O, -CH(D)OD is formed selectively (36). The mechanism proceeds via a phosphonium species formed by initial nucleophilic attack of the P-atom at the carbonyl C-atom, i.e., via ArCH(OH)P%, where Ar is the aromatic residue and R is the hydroxyalkyl substituent (36). When the aldehyde contains a 4-OH substituent, the alcohol product... 

The homoallylation product 16a presumably stems from oxidative cycloaddition of a Ni(0) species across the diene and aldehyde moieties of 15, leading to an oxanickellacycle intermediate 17 (path A, Scheme 5), which undergoes 0-bond metathesis with triethylsilane giving rise to a o-allylnickel 19. On the other hand, formation of 16b may start with addition of a Ni - H species upon the diene followed by intramolecular nucleophilic allylation as described in Eqs. 4-6 (path B). Alternatively, allylic transposition of the NiH group providing 20 from 19 may be related to the formation of 16b. The different reactivity between cyclohexadiene and many other acyclic dienes is also observed for the reaction undertaken under typical homoallylation conditions (see Scheme 14). 

A rationale for the cz s-selective cyclization for the intramolecular homoal-lylation of oo-dienyl aldehyde 64 is illustrated in Scheme 16. The scenario is essentially the same as the one proposed for the intermolecular reaction, and a Ni(0) species undergoes oxidative addition upon the diene and the aldehyde moieties through a conformation placing the aldehyde substituent and the diene anti to each other. An intermediate 66 undergoes (>-II elimination and czs-reductive elimination of the thus-formed Ni - H complex to produce 65. 

Although the mechanistic details will be difficult to elucidate, the catalytic system, operating at ambient thermal conditions, appears to have considerable potential in synthesis for removing CO groups from aldehyde moieties of sensitive organic compounds. 

High stereoselectivity was also observed in the reaction of organocopper reagents 215 with the aldehyde moiety of (774-diene)Fe(CO)3 complexes 214 (Scheme 98).491... 

As yet, there are not many examples of this. As a representative example, the reaction of zirconacyclopentadienes with aldehydes in the presence of A1C13 affords cyclopentadiene derivatives. In this case, the aluminum abstracts the oxygen atom from the aldehyde moiety (Eq. 2.31) [11]. Aluminacyclopentadiene might be the intermediate in this reaction. 

When allenyl aldehydes are allowed to react with DMDO, the aldehyde moiety is not oxidized to the acid except for monosubstituted allenes [21]. In all other cases, the carbonyl oxygen participates as a nucleophile in the opening of the intermediate epoxide. From 2,2,5-trimethy]-3,4-hexadienal 67, for example, five different products can be synthesized selectively under different reaction conditions (Scheme 17.22). When p-toluenesulfonic acid (TsOH) is present or DMDO is formed in situ, then the initially formed allene (mono)oxide reacts with the aldehyde moiety to give 68 or 69. In the presence of excess DMDO and the absence of acid, three other products (70-72) can be formed via the spirodioxide intermediate. These reactions, however, seem to be less general compared with similar reactions of allenyl acids and allenyl alcohols. y-Allenylaldehydes 73 can be cyclized to five-membered hemiacetals 74 via the spirodioxide intermediate. 

Rather, the conformational bias in our substrates is apparently dependent on a very particular relationship between the formyl moiety and unsaturated in the pendant side chain. As a result of our studies, we speculate that the presence of unsaturation at C4-C5 in the aldehyde moiety provides a subtle stabilizing nonbonded interaction between the unsaturation in the aldehyde and the carbonyl of the enolate (Table 2.1,... 

The a-silyloxy alkyl radical generated by the addition of (TMS)3Si radical to the aldehyde moiety of 45 has been employed in radical cyclization of (3-aminoacrylates (Reaction 7.53) the trans-hydroxy ester and the lactone in a 2.4 1 ratio were the two products [62]. 

Major oxidation products of propanolol and metoprolol formed during ozonation in aqueous solution were investigated by Benner et al. [102, 103]. In the case of propanolol, the main ozonation product is a ring-opened compound with two aldehyde moieties, which results from ozone attack to the naphthalene ring [103]. Formation of aldehyde moieties was also one of the main oxidation routes during metoprolol ozonation, together with hydroxylation [102]. 

The reagent is highly selective, as demonstrated by the inertness of several sensitive functionalities such as amino, hydroxyl, azo, hydrazo, phenol, sulphide, disulphide, sulphoxide, aldehyde moieties, and olefmic and acetylenic carbon-carbon bonds. The ability of the reagent to differentiate thiols may be used to prepare unsymmetrical disulphides. 

The a,(3-unsaturated aldehyde moiety in these molecules was responsible for their fungicidal action (5). This was described to result from the structural disruption of the cell membrane (6). (Adapted from Kubo et ah, 2001)... 

Annulation of the pyrrole ring. o-Aminoketone 179, bearing the protected aldehyde moiety, can be smoothly reacted with substituted phenyl alanines and transformed into 1,4-benzodiazepinones 180 with a fused pyrrole ring (Scheme 36 (1992BMCL1639)). 

Scheme 11 Under mild conditions, oxidation of HMF in methanol can be tuned to yield methyl (5-hydroxymethyl)-furoate via oxidation of the aldehyde moiety.

Furfural. Furfural is readily obtainable from dehydration of pentoses. Reduction of furfural can lead to a variety of products that are more volatile, more stable and possibly also more useful than furfural itself. Selective reduction of the aldehyde moiety leads to furfuryl alcohol (Scheme 15), whereas further reduction of the furan core will lead to tetrahydrofurfuryl alcohol. Reductive deoxygenation can result in the formation of either 2-methylfuran or 2-methyltetrahydrofuran, which can be used as liquid fuels or solvents. 

Resin-bound 4/7-1,3-oxazines 115 were synthetized by the stepwise condensation of an amide resin 489, an aldehyde, and an alkyne. Formation of the oxazine ring took place in the presence of the catalyst BF3-Et20 via a hetero-Diels-Alder cycloaddition of the alkyne and the acyliminium 491 arising from the condensation of the amide and the aldehyde (Scheme 92). The quantitative efficacy of the process was determined by elemental analysis of a model system bearing a bromine atom on the aldehyde moiety (R =C6H4Br(p)), which indicated a 78% conversion for the heterocyclization <2001CEJ2318, 2004JC0846>. 

The oxygen atom has also been used to generate other functionalities, such as the aldehyde moiety in Kibayashi s syntheses of (—)-coniine (197) and its enantiomer (Scheme 1.43) (253). Here, reaction of tetrahydropyridine N-oxide 93 with a silylated chiral allyl ether dipolarophile 198 delivered the adduct 199 with the desired bridgehead stereochemistry via the inside alkoxy effect . Desilylation and hydrogenolytic N—O bond rupture with palladium(II) chloride provided the diol 200... 

The aldehyde moiety of 50 can be condensed with either amines or active methylene compounds. In the case of reactions with amines, the aldehyde 50 (presumably obtained by reduction of the cyano group with diisobutyl-aluminium hydride (DIBAL-H)) forms simple Schiff bases 51 (Equation 20) <1998J(P1)3557>. 

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