Aldehydes 2- benzaldehyde

Aldehydes undergo condensation with primary amines with the elimination of water to give compounds known as SchifF s Bases, which can also be used to characterise aldehydes. Benzaldehyde for example condenses readily with... 

In 1949, Comforth showed that preparation of 2,5-disubstituted oxazoles was not limited to diaryloxazoles through condensation of aldehydes (benzaldehyde, n-hept-aldehyde) with a-hydroxy-amides (lactamide). The intermediate oxazolidone 13 were converted into oxazoles 14 on warming with phosphoryl chloride. ... 

Pyruvic Acid Compounds.—Lubrzynska and Smedley have recently shown that a number of aldehydes such as heliotropin, anisic aldehyde, benzaldehyde, and cinnamic aldehyde, condense with pyruvic acid in slightly alkaline solution, with the formation of )8-unsaturated-a-ketonic acids. For example, if heliotropin and pyruvic acid in alkaline solution be left standing for about eight days at ordinary temperature, dihydroxy-methylene-benzal-pyruvic acid is formed. This body forms yellow needles, melting at 163° Similarly, anisic aldehyde yields methoxy-benzal-pyruvic acid, melting at 130° and cinnamic aldehyde yields cinnamal-pyruvic acid, melting at 73°. 

Aromatic aldehydes. Benzaldehyde, vanillin, and cinnamaldehyde are aldehydes with pleasant aromas that are found in almonds, vanilla beans, and cinnamon, respectively. 

Standard transformations at the a-carbon, as discussed in CHEC-II(1996) <1996CHEC-II(4)179>, proceed without incident. Selected recent examples (Scheme 19 Equation 22) include the conversion of the esters 153 into the hydrazides 154 and thence into the methylene carbohydrazides 155 <2005HC029>, a process that has been shown by the same workers to apply to other aldehydes (benzaldehyde, 4-A Ar-dimethylaminobenzaldehyde, furfuralde-hyde, or thiophene 2-carboxaldehyde) with equal success <1999FES747>, and the conversion of the ester 156 into amide 157 <2005NN1919>, a process that demonstrates the robustness of the 1,2,4-oxadiazole ring. 

This motif is easily accessible from the condensation under acidic conditions of substituted hydroxymethyl pyrroli-done with a ketone, an aldehyde, or a masked ketone or aldehyde. Benzaldehyde <1996T3719, 1999JA10478, 2002JOC8688>, methoxypropene <1998T10295>, and dimethoxypropane <2001JOV8831, 2002TA647,... 

Aromatic aldehydes (benzaldehyde and its derivatives) are prepared from aromatic hydrocarbons by the following methods ... 

In einer Zweistufen-Variante der Schweizer-Reaktionlassen sich l-Amino-2-alkene mit fast ausschlieBlicher oder liberwiegender (E)-Struktur herstellen, indem man Aldehyde (Benzaldehyde, Zimtaldehyd, Furfural) in Tetrahydrofuran mit Ethenyl-tributyl-phospho-nium-bromid, Phthalimid und Natrium-hydrid (-fPhthalimid-natrium) umsetzt und das so erhaltene, N-substituierte Phthalimid mit Hydrazin spaltet oder mittels Natriumsulfid/ Wasser in Phthalsaure-monoamide uberfuhrt und diese mittels waBriger Oxalsaure spaltet1. Bei Zusatz von Lithiumbromid in der 1. Stufe erhalt man uberwiegend die (Z)-Iso-meren. 

The simplest araliphatic aldehyde, benzaldehyde and its 4-isopropyl homologue, cuminaldehyde, are used to a limited extent as fragrance and flavor materials. However, both compounds are used in large quantity for the production of the corresponding cinnamic and dihydrocinnamic aldehydes. 

Figs. 7.1-7.4), which are responsible for a spicy, floral and fruity characteristic of stone fruits [17, 64, 71, 72]. Ca compounds are the major volatiles in immature, green fruits but the levels of these compounds decrease drastically during maturation, and lactones (lactonic note), aldehydes (benzaldehyde with an almond, nutty and stone fruit note), terpenes (linalool with a floral note) and esters become prominent [14,15, 65, 66, 68, 70]. 

Identify the C=O absorptions in the spectra of these esters and note the effect of conjugation on the C=O stretch. You should also identify, and compare the wavenumbers of, the C—O absorptions of 2-methy propanal (Figure 3.14) and the conjugated aldehyde benzaldehyde (Figure 3.2). 

Most of the studies on Botrytis-specific aroma compounds have investigated the aroma composition of wines (Table 6.7). Only a few have focused on what occurs in the grape. On synthetic media, the main odorous compounds produced by B. cinerea are aromatic aldehydes (benzaldehyde, phenylacetaldehyde), and furfural (Kikuchi et al., 1983). Sarrazin et al. (2007a) confirmed the higher concentration of phenylacetaldehyde in noble-rotted grapes. 

Essential Oils Cinnamic Aldehyde Benzaldehyde + Ethanal... 

Two new chiral carbon atoms are formed in the condensation and four diastereoisomeric p-sulfinyl y-lactones can therefore in principle be obtained. However, only two dia-stereoisomers, (3S,4, s ) and (3R,4S,Rs), are isolated when the carbanion is condensed with pivalic aldehyde, benzaldehyde, or pinacolone (yield 65-70% for aldehydes, ratio 53 47 yield 47% for pinacolone, ratio 81 19). The diastereoselectivity decreases when the two substituents of the carbonyl group are sterically similar. However, single diastereoisomers can easily be separated through chromatography and transformed in high yield into both enantiomers of optically pure saturated (by desulfurization) and a,(3-unsaturated y-lactones (by pyrolytic sulfoxide elimination) (eq 3). The relative and absolute stereochemistry of all the products have been determined by circular dichroism, nuclear Over-hauser effects, and X-ray analyses. 

Cyanogen and ca-bromoacetophenone give di-imino-dihydroquimxaline and a phenyl-dihydroquinoxaline respectively. If the diketones are replaced by monocarbonyl compounds such as aldol, crotonie aldehyde, benzaldehyde, o- and p-anisaldehydes or iiiperonal, arsenated Schiff s bases result, e.g. 

Aromatic aldehydes react with 196, probably through the intermediate 197 in acetic acid or anhydride, without addition of base. This reaction, which leads to cations 198, has-been performed with various aldehydes benzaldehydes, cinnamaldehydes, salicylaldehydes, - " and 2-phenyl-4//-l-benzopyran-3-carbaldehyde. Similar reactions occur with ketones and pyrones but need a strong base as catalyst. 

A solvent effect on diastereoselectivity was also observed with other substrates (Table XVIII). Generally, when aromatic aldehydes (benzaldehyde, furfural, 2-thiophenecarbaldehyde) and benzaldehyde dimethyl acetal were used, the ratio of threo to erythro products increased in the following order... 

Cinnamyl alcohol Formic acid (11) 60 Glycolic aldehyde Benzaldehyde a-Ethoxypropional Formaldehyde 77 84 96 96.2... 

Upon treating certain (but not all) aromatic aldehydes or glyoxals (a-keto aldehydes) with cyanide ion (CN ), benzoins (a-hydroxy-ketones or acyloins) are produced in a reaction called the benzoin condensation. The reverse process is called the retro-benzoin condensation, and it is frequently used for the preparation of ketones. The condensation involves the addition of one molecule of aldehyde to the C=0 group of another. One of the aldehydes serves as the donor and the other serves as the acceptor. Some aldehydes can only be donors (e.g. p-dimethylaminobenzaldehyde) or acceptors, so they are not able to self-condense, while other aldehydes (benzaldehyde) can perform both functions and are capable of self-condensation. Certain thiazolium salts can also catalyze the reaction in the presence of a mild base. This version of the benzoin condensation is more synthetically useful than the original procedure because it works with enolizable and non-enolizable aldehydes and asymmetric catalysts may be used. Aliphatic aldehydes can also be used and mixtures of aliphatic and aromatic aldehydes give mixed benzoins. Recently, it was also shown that thiazolium-ion based organic ionic liquids (Oils) promote the benzoin condensation in the presence of small amounts of triethylamine. The stereoselective synthesis of benzoins has been achieved using chiral thiazolium salts as catalysts. 

Composition 65-80% (E)-ciimamaldehyde, up to app. 10% eugenol, methyl eugenol, linalool, which, has been reported not to occur in cassia oil [56], (E)-cirmamyl acetate, geranylacetate, benzyl benzoate, caryophyllene, hydrocirmamic aldehyde, benzaldehyde, a-terpineol, pinene, phellandrene, p-cymene and others [57, 58, 59], Note that Cinnamon bark and leaf oil are also specified in the European Pharmacopoeia. 

In 1991, Mukaiyama et al. reported that high enantioselectivity can be achieved using the chiral tin (II) complex 6 derived from cinchonine (Cn) as a Lewis acid catalyst in the reactions of aldehydes and TMSCN [28]. However, the utilization of this protocol is limited to aliphatic aldehydes, where up to 96% ee was obtained (Table 4.4). However, when this protocol was applied to an aromatic aldehyde (benzaldehyde), no reaction was observed with TMSCN under the same conditions. 

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