Olefination cinnamic acid preparation

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

Olefinic acids prepared by this method include y0,yS-dimethylacrylic acid (53%) from mesityl oxide, cinnamalacetic acid (70%) from cinnamal-acetone, and tra s-a-alkylcinnamic acids from the corresponding methyl ketones (80%). ... 

The preparation of chelating surface-active diphosphines proved to be more successful. The BDPP analogue R,R-(9) was synthesized by lithiation of tris[p-(3-phe-nylpropyl)phenyl]phosphine, reaction with (R,R)-2,4-pentane-diylditosylate and subsequent sulfonation with concentrated sulfuric acid [16]. Hydrogenation of the prochiral olefin (Z)-2-(N-acetamido)cinnamic acid ester in a two-phase system (ET0Ac/H20) with Rh complexes derived from R,R-(9) was accomplished with identical selectivity compared with the unsulfonated BDPP and improved reactivity compared with BDPPTS (2). 

Pans-2-Iodocyclohexyl acetate can be isolated in essentially quantitative yield from the reaction of thallium(I) acetate, iodine, and cyclohexene in a 1 1 1 molar ratio in refluxing chloroform. lodo acetates from a representative series of alkenes including cyclohexene have been similarly prepared in 80-98% yield in glacial acetic acid which was not dried as described in this procedure. The corresponding iodo benzoates are obtained in comparable yields from reaction with thallium(I) benzoate and iodine in benzene. The deactivated olefin methyl cinnamate did not react under these conditions, and o-allylphenol underwent ring iodination to... 

Cinnamic esters or amides prepared from optically active alcohols (menthol, aryl ethanol) or amines are hydrogenated to products in only low optical yields (less than 40%). Camphor sultam is a much better rr-face discriminator and the hydrogenation of the trisubstituted olefinic bond of sultam-imides over Pd-on-carbon affords, after saponification, j3-substituted carboxylic acids in high e.e. (>95%) ... 

One of the standard methods for preparing enantiomerically pure compounds is the enantioselective hydrogenation of olefins, a,/3-unsaturated amino acids (esters, amides), a,/3-unsaturated carboxylic acid esters, enol esters, enamides, /3- and y-keto esters etc. catalyzed by chiral cationic rhodium, ruthenium and iridium complexes ". In isotope chemistry, it has only been exploited for the synthesis of e.p. natural and nonnatural H-, C-, C-, and F-labeled a-amino acids and small peptides from TV-protected a-(acylamino)acrylates or cinnamates and unsaturated peptides, respectively (Figure 11.9). This methodology has seen only hmited use, perhaps because of perceived radiation safety issues with the use of hydrogenation procedures on radioactive substrates. Also, versatile alternatives are available, including enantioselective metal hydride/tritide reductions, chiral auxiliary-controlled and biochemical procedures (see this chapter. Sections 11.2.2 and 11.3 and Chapter 12). 

---