4- hexenoic acid

The intramolecular reaction oF allcenes with various O and N functional groups offers useful synthetic methods for heterocycles[13,14,166]. The reaction of unsaturated carboxylic acids affords lactones by either exo- or endo-cyclization depending on the positions of the double bond. The reaction of sodium salts of the 3-alkenoic acid 143 and 4-alkenoic acid 144 with Li2PdCl4 affords mostly five-membcrcd lactones in 30-40% yields[167]. Both 5-hexe-noic acid (145) and 4-hexenoic acid (146) are converted to five- or six-mem-bered lactones depending on the solvents and bases[168]. Conjugated 2,4-pentadienoic acid (147) is cyclized with Li2PdCl4 to give 2-pyrone (148) in water[i69]. 

Conjugated Double Bonds. Sorbic acid is brominated faster than other olefinic acids (7). Reaction with hydrogen chloride gives predominately 5-chloro-3-hexenoic acid (8). 

Similar coordination occurs also in the presence of other di- and trivalent metals. Reduction of the double bonds can produce various hexenoic acid mixtures. 

Sorbic acid anhydride [13390-06-2] can be prepared by heating the polyester of 3-hydroxy-4-hexenoic acid with sorboyl chloride [2614-88-2] or by reaction of sorbic acid with oxalyl chloride (15,16). Preparation of the esters of sorbic acid must be controlled to prevent oxidation and polymerization. The lower sorbic acid esters have a pleasant odor. 

Other methods include ring opening of parasorbic acid [108-54-3] (5-lactone of 5-hydroxy-2-hexenoic acid) in hydrochloric acid or in alkaline solutions (43,44), the ring opening of y-vinyl- y-butyrolactone in various catalysts (45,46), or isomerization of 2,5-hexadienoic acid esters (47,48). Other methods are described in thehterature (6,49,50). 

An example of a stereoselective hydrogenation in ionic liquids was recently successfully demonstrated by Drie en-H6lscher et al. On the basis of investigations into the biphasic water/n-heptane system [51], the ruthenium-catalyzed hydrogenation of sorbic acid to cis-3-hexenoic acid in the [BMIM][PFg]/MTBE system was studied [52], as shown in Scheme 5.2-8. 

Methyl-2-hexenoic acid (mixture of ll and Z isomers) has been identified as the substance responsible for the odor of human sweat. Synthesize the compound from starting materials having five or fewer carbons. 

CN ( )-6-(l,3-dihydro-4-hydroxy-6-methoxy-7-methyl-3-oxo-5-isobenzofuranyl)-4-methyl-4-hexenoic acid 2-(4-morpholinyl)ethyl ester... 

Sorbic acid has been prepared from crotonaldehyde 1 5 or aldol6 and malonic acid in pyridine solution by hydrogen peroxide oxidation of the condensation product of crotonaldehyde and pyruvic acid 7 and by the action of alkali on 3-hydroxy-4-hexenoic acid,8 9 /3,5-disulfo-w-caproic acid,10 and parasorbic acid.1112... 

Figure 11.2 Py/silylation GC/MS chromatograms of aged linseed oil pyrolysed in the pre sence of HMDS, (a) Pyrogram obtained with a microfurnace pyrolyser pyrolysis temperature 600 °C furnace pressure 14 psi purge flow 0.5 ml min (b) Pyrogram obtained with a resistively heated filament pyrolyser pyrolyser interface I80°C transfer line 300°C valve oven 290°C. 1, Hexenoic acid, trimethylsilyl ester 2, hexanoic acid, trimethylsilyl ester 3, heptenoic acid, trimethylsilyl ester 4, heptanoic acid, trimethylsilyl ester 5, octenoic acid, trimethylsilyl ester 6, octanoic acid, trimethylsilyl ester 7, nonenoic acid, trimethylsilyl ester 8, nonanoic acid, trimethylsilyl ester 9, decanoic acid, trimethylsilyl ester 10, lauric acid, trimethylsilyl ester 11, suberic acid, trimethylsilyl diester 12, azelaic acid, trimethylsilyl diester 13, myristic acid, trimethylsilyl ester 14, sebacic acid, trimethylsilyl diester 15, palmitic acid, trimethylsilyl ester 16, stearic acid, trimethylsilyl ester...

Again, addition of trialkylphosphine was found to be effective for reducing the amount of products obtained by attaching a formyl group to a carbon other than that of the original carbon-carbon double bond (73). Results obtained with hexenoic acid esters are outlined in Table XXIV. 

Table 14.3 Hydrogenation of methyl sorbate to 3-hexenoic acid methyl ester with [Cr(CO)3(arene)] (45) catalysts.

The various isomeric hexenoic acids are useful starting materials for the production of fine chemicals, and the stereoselective hydrogenation of sorbic acid has attracted considerable interest. It was shown recently that this reaction could be catalyzed by [Ru(CO)(Cp )(mtppts)] [CF3SO3] (Cp =//5-C5Me5) in a water -heptane biphasic mixture to yield tra s-3-hexenoic acid with up to 85% selectivity [39] (Scheme 38.3). Conversely, the use of [ RuC12(PR3)2 2] (R=CH2CH2CH2OH) as catalyst precursor led to the selective formation of 4-hexenoic acid [40]. 

A special example for a regioselective hydrogenation in ionic liquids was reported by our group and by DrieRen-Holscher [96, 97]. Based on investigations in the biphasic system water/n-heptane, the ruthenium-catalyzed hydrogenation of sorbic acid to ds-3-hexenoic acid according to Scheme 41.3 in the system [BMIM][PF6]/MTBE was studied [98],... 

In comparison to polar organic solvents (e.g., glycol), a more than threefold increase in activity with comparable selectivity to ds-3-hexenoic acid was ob-... 

Hexenoic acid, physical properties, 5 31t lrans-2-Hexenal, transport through barrier... 

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