Dienal

Aldehydes, enals, dienals, ketones, and hydrocarbons, which are responsible for disagreeable odors, generally bok at lower temperatures than fatty acids. Analysis showkig a free fatty acid concentration of less than 0.05% is an kidication that deodorization is sufficientiy complete. Some of the dienals have very low odor thresholds and sensory evaluation of the finished ok is a judicious quaHty assurance step. 

Hence the compound is nona-2,6-dienal. The relative configuration of both CC double bonds follows from the HH coupling constants of the alkene protons in the H NMR spectrum. The protons of the polarised 2,3-double bond are in trans positions Jhh 5.5 Hz) and those on the 6,7-double bond are in cis positions Jhh = 10.5 Hz). The structure is therefore nom.-2-tmns-6-cis-dienal, D. 

CoCl2 6H20 [149] or TMSOTf 20 [150-152] in acetonitrile afford Diels-Alder adducts in yields of up to 85%. The dienals 607 are converted by bis(trimethyl-silyl)thiane 601 or bis(trimethylsilyl)selenide 604 and catalytic amounts of BuLi, via 609, to the intramolecular Diels-Alder products 610 in up to 70% yield [153, 154]. 

Figure 1.10 Aldehydic regions of 400 MHz H-NMR spectra of unheated (a) and repeatedly used samples (b) of culinary frying oil obtained from a fast-food/take-away establishment. A total of 0.30 ml of each sample was diluted to a final volume of 0.90 ml with C HCls. High levels of n-alkanals, trans-2-alkenals and alka-2,4-dienals are detectable in spectrum (b).

Model systems indicate that aldehydes may also be produced by the action of polyphenoloxidases on amino acids in the presence of catechin, all of which are present in coffee beans at some stage between green and roasted. For example, valine yields isobutanal, leucine yields isopentanal, and isoleucine yields 2-methyl-butanal.14 Some of these aldehydes probably undergo condensation reactions in the acidic medium of the roasted bean when moisture is present.15 Some dienals in green coffee beans have recently been identified as (E,E)-2,4- and (E,Z)-2,4-nonadienal and (E,E)-2,4- and (E,Z)-2,4-decadienal.18... 

Scheme 9 shows SvatoS s synthesis of (8Z, 10 )-tetradeca-8,10-dienal (3), the female pheromone of the horse-chestnut leafminer (Caneraria ohridella) [20]. Palladium-catalyzed coupling of A with 1-pentyne was the key-step. 

Cinnamic acid esters can be converted to dienals via Grignard addition and Vilsmeier reaction (equation 184)306. 

H6]-Leukotriene A4 methyl ester, 17, has been synthesized14 by Wittig olefination of epoxy dienal 18 with the key reagent 3,4,6,6,7,7-[2H6]-(Z)-(3-nonen-1-yl)triphenylphosphonium iodide, 19 (equation 9). 17 is employed as stable isotope internal standard for the MS trace analysis of eicosanoids15-17. 

A ruthenium(n)-indenyl complex, which is an efficient catalyst for the isomerization of allylic alcohols, is also an effective catalyst for the isomerization of propargylic alcohols to both a,/3-enals and a,/ -enones (Scheme 57).96 In this reaction, the addition of 20—40 mol% InClj is highly effective. The reaction exhibits extraordinary chemoselectivity and a variety of functional groups are unaffected, which allows a highly efficient synthesis of dienals (R1 =Me2C = CH, R2 = H). 

Alternatively, Cl of the diradical can abstract H- from C4 in a disproportionation reaction to give the dienal product. 

Table 6 gives the calculated and experimental 13C shieldings for acrolein, crotonalde-hyde and hexa-2,4-dienal. The numbering of the carbon atoms is given in Figure 1. The calculated and experimental 13C chemical shift data were converted to the methane reference using the data in Table 7 and in the standard reference17, respectively. 

Isolated double bonds can be oxidatively cleaved in systems containing a conjugated diene moiety if it is protected as a tricarbonyl(diene)iron complex44. Dienal 39 was acquired in 49% yield by a two-step osmylation-periodate cleavage sequence (equation 27). In contrast, ozonolysis of the polyene complexes is reported to lead to destruction of the complex. 

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