Aldehydes occurrence

Feron VJ, Til HP, de Vrijer F, et al. 1991. Aldehydes occurrence, carcinogenic potential, mechanism of action and risk assessment. Mutat Res 259 363-385. 

In the discussion of some mass spectra of nitrones (41), intermediate isomerization to oxaziridines was concluded from the occurrence of aldehyde fragments. 

I) derived from this by dissociation, or in a mobile equilibrium mixture of both these forms. Dobbie et reproduced the spectra of cotarnine solutions containing varying amounts of potassium hydroxide by using cotarnine chloride and hydrocotamine and by dissolving mixtures of the latter two compounds or by placing the separate solutions of these compounds in the apparatus in series. Thus no evidence could be obtained for the occurrence of the amino-aldehyde (3) postulated by Roser. Steiner, Kitasato, and Skinner came to similar conclusions. The band at 285 m/x in alkaline solutions is not due to an aromatic aldehyde. This band also occurs in the spectrum of hydrocotamine (10a) and in the carbinolamine... 

A detailed NMR study and determination of the X-ray structure of the ligand has suggested the occurrence of 7t-stacking of the 2,6-diisopropoxybenzene ring and coordinated aldehyde [5 c]. Because of this stacking, the si face of the CAB-co-ordinated a,/ -unsaturated aldehyde is sterically shielded (Fig. 1.1). 

The aldehydes of the geraniol series are of very great commercial importance. The only two which are of common occurrence are citral and citronellal. 

The aldehydes of the cyclic series include a number of compounds which are of common occurrence in essential oils, and a certain number which are prepai ed synthetically for perfumery purposes. 

The widespread occurrence and biological significance of polyoxygenated carbocycles provided the impetus to apply RCM to sugar-derived dienes. Carbohydrate carbocyclization based on a sequence of Vasella reductive opening of iodo-substituted methyl glycosides [25], and RCM of the dienes available from the resulting unsaturated aldehydes, were used to prepare a series of natural compounds (Schemes 5-7). 

All the oxidants convert primary and secondary alcohols to aldehydes and ketones respectively, albeit with a great range of velocities. Co(III) attacks even tertiary alcohols readily but the other oxidants generally require the presence of a hydrogen atom on the hydroxylated carbon atom. Spectroscopic evidence indicates the formation of complexes between oxidant and substrate in some instances and this is supported by the frequence occurrence of Michaelis-Menten kinetics. Carbon-carbon bond fission occurs in certain cases. 

The chlorophylls share a common tetrapyrrole stmcture and in their normal occurrence contain a chelated magnesium ion [28,29]. Structures for some chlorophyll a and b are shown in Figure 13.3. The structural difference is that there is a methyl group in chlorophyll a, whereas there is an aldehyde function in chlorophyll b. The... 

Esterbauer, H., Zollner, H. and Schaur, KJ. (1990). Aldehydes formed by lipid peroxidation mechanisms of formation, occurrence and determination. In Lipid Oxidation (ed. C. Vigo-Pelfrey) pp. 239-283. CRC Press, Boca Raton, FL. 

Traditional models for diastereoface selectivity were first advanced by Cram and later by Felkin for predicting the stereochemical outcome of aldol reactions occurring between an enolate and a chiral aldehyde. [37] During our investigations directed toward a practical synthesis of dEpoB, we were pleased to discover an unanticipated bias in the relative diastereoface selectivity observed in the aldol condensation between the Z-lithium enolate B and aldehyde C, Scheme 2.6. The aldol reaction proceeds with the expected simple diastereoselectivity with the major product displaying the C6-C7 syn relationship shown in Scheme 2.7 (by ul addition) however, the C7-C8 relationship of the principal product was anti (by Ik addition). [38] Thus, the observed symanti relationship between C6-C7 C7-C8 in the aldol reaction between the Z-lithium enolate of 62 and aldehyde 63 was wholly unanticipated. These fortuitous results prompted us to investigate the cause for this unanticipated but fortunate occurrence. 

Additional aldehydes and ketones were also included in the U.S. Nationwide Occurrence Study dimethylglyoxal (2,3-butanedione), cyanoformaldehyde, 2-butanone (methyl ethyl ketone), trans-2-hexanal, 5-keto-l-hexanal, and 6-hydroxy-2-hexanone [11, 13]. Dimethylglyoxal was the most consistently detected of these carbonyl compounds (up to 3.5 pg/L) and was found at higher levels in plants using ozone. Maximum levels of 0.3, 5.0, and 0.7 pg/L were observed for cyanoformaldehyde, 2-butanone, and trans-2-hexenal, respectively 6-hydroxy-2-hexanone and 5-keto-1 -hexanal were only detected in early stages of treatment, and not in finished waters. 

A variety of methods have been developed for the preparation of substituted benzimidazoles. Of these, one of the most traditional methods involves the condensation of an o-phenylenediamine with carboxylic acid or its derivatives. Subsequently, several improved protocols have been developed for the synthesis of benzimidazoles via the condensation of o-phenylenediamines with aldehydes in the presence of acid catalysts under various reaction conditions. However, many of these methods suffer from certain drawbacks, including longer reaction times, unsatisfactory yields, harsh reaction conditions, expensive reagents, tedious work-up procedures, co-occurrence of several side reactions, and poor selectivity. Bismuth triflate provides a handy alternative to the conventional methods. It catalyzes the reaction of mono- and disubstituted aryl 1,2-diamines with aromatic aldehydes bearing either electron-rich or electron-deficient substituents on the aromatic ring in the presence of Bi(OTf)3 (10 mol%) in water, resulting in the formation of benzimidazole [119] (Fig. 29). Furthermore, the reaction also works well with heteroaromatic aldehydes. 

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