Protection with cinnamaldehyde

Anm Ghosh used aminoindanol as the chiral auxEiary. The titanium enolate was formed by reaction of the ester with titanium tetrachloride and diisopro-pylethylamine. This was reacted at -78 °C with cinnamaldehyde, pre-complexed with Bu2BOTf. The desired anti-enantiomer was obtained in a 6.1 1 excess. The diastereomers were separated by colmnn chromatography. The chiral auxEiary was subsequently cleaved off in a very mEd procedure with lithium hydroperoxide. Attempts to protect the hydroxy-carboxylic acid in the usual way, with pivalaldehyde in presence of camphor-lO-siEfonic acid or p-toluenesulfonic acid, faded. EventuaUy, isopropoxytrimethylsEane, TMSOTf and molecular... 

In 1996, Liu et al. reported the selective hydrogenation of cinnamaldehyde, an a,/ -unsaturated aldehyde, to cinnamyl alcohol, an a,/ -unsaturated alcohol, by means of PVP-protected Pt/Co bimetallic colloids prepared by the polyol process [111]. The colloids were obtained as a dark-brown homogeneous dispersion in a mixture of ethylene glycol and diethylene glycol, and characterized by TEM and XRD. These authors prepared different samples of nanoparticles with Pt Co ratios of 3 1 and 1 1, the mean diameters of which measured 1.7 and 2.2 nm, respectively. These colloidal systems were also compared with the single metal-... 

An alkoxy-substituted cinnamyl system 44 is transiently generated by the treatment of cinnamaldehyde 42 with lithiated trimethylethylenediamine 43, and this protected version of cinnamaldehyde undergoes carbolithiation with good diastereoselectivity in favour, like 32, of the syn product 45.30... 

Dithioacetals are useful in organic synthesis as protective groups for carbonyl compounds, as precursors of acyl carbanion equivalents or as electrophiles under Lewis acidic conditions. The DBSA-catalysed system was also found to be applicable to dithioacetal-ization in water. In addition, easy work-up has been realized without the use of organic solvents when the products are solid and insoluble in water. In fact, the dithioacetaliza-tion of cinnamaldehyde on 10 mmol-scale with 1 mol% of DBSA proceeded smoothly to deposit crystals. The pure product was obtained in excellent yield after the crystals were filtered and washed with water (Equation (8)). This simple procedure is one of the advantages of the present reaction system. 

The first asymmetric total synthesis of acosamine and daunosamine starting from a nonsugar precursor was reported by Fuganti and co-workers [288,289,290,291]. They found that baker s yeast catalyzes the asymmetric pinacolic cross-coupling of cinnamaldehyde and ethenal giving a ft-diol 156. This diol is protected as an acetonide and submitted to ozonolysis giving L-157. Olefination of L-157 with PhsP = CHCOOMe, followed by treatment with ammonia, provides 158 that is then converted into W-trifluoroacetylacosamine 158 (O Scheme 61). 

Although most synthetic approaches to L-daunosamine start from carbohydrate precursors, some routes employ chiral synthons derived from other sources. The aldehydes 213 obtained through reaction of cinnamaldehyde with acetaldehyde in the presence of Baker s yeast followed by ozonolysis [157], and 214 obtained from L-tartaric acid [158-160] have been utilised in the synthesis of daunosamine derivatives, and protected daunosamines and acosamines have been synthesised from (synthetic approaches have employed lactic acid as a chiral starting material [162, 163] and the (S)-amine 215 obtained by resolution has been converted to V-benzoyl daunosamine together with its 3-epimer [164]. Wovkulich and Uskokovic have... 

The reversibility problem in 1,2-additions is alleviated when imines bearing an electron-poor protecting group at nitrogen (sulfonyl, aeyl, ear-bamoyl) are employed as aeceptor partners, rendering possible even the use of 1,3-dicarbonyl compounds as donors. For example, Sehaus and eoworkers reported the highly enantioselective Mannich reaction of acetoacetates and cyclic 1,3-dicarbonyl compounds with N-carbamoyl imines derived from benzaldehydes and cinnamaldehydes catalysed by the natural Cinchona alkaloid cinchonine (CN) (Scheme 14.15). On the basis of the obtained results they developed a model that accounts for the observed diastereo- and enantioselectivity based on the bifunctional nature of the catalyst, which acts simultaneously as a hydrogen-bond donor and acceptor. 

The following example illustrates how the corrosion efficiency of an inhibitor can be evaluated with LPR. Forty years ago, Hugel tested a variety of inhibitors for steel in 6 M HCl at 60°C and found that alkenyl and aromatic aldehydes were very effective [11]. Cinnamaldehyde was one of the best, providing almost 99 percent protection. Numerous patents have been issued since then on the use of aldehydes, and trans-cinnamaldehyde (TCA) in particular, as steel corrosion inhibitors in acid media have been used to reduce the corrosion of steel during pickling or oil field acidizing treatments. 

Some corrosion inhibitors have properties that are normally associated with surfactants. Recently, Pebere et al. studied 2-hexadecylimidazoline and 2-hexadecy-iimidazole as inhibitors of a carbon steel in HCI containing H2S, and they obtained a protection vs. inhibitor concentration profile similar to that often seen with cationic surfactants that is, there was a sharp increase in protection below the critical micelle concentration (CMC) followed by a leveling off at the CMC. Above the CMC, the inhibitors appear to form thick adherent films that act as diffusion barriers. In contrast, a study of the effects of ethoxylated alcohols (nonionic surfactants) and quaternary nitrogen salts (cationic surfactants) on the performance of the inhibitor cinnamaldehyde on mild steel in 15% HCI indicates that in these cases the surfactants co-adsorb with the inhibitor and produce a maximum effect far below their CMCs. ... 

Oxygen-containing inhibitors that are successful in concentrated HCl include cinnamaldehyde and the alkynols containing unsaturated groups conjugated with the oxygen function described as alpha-alkenylphenones. They provide, especially when mixed with small amounts of surfactants, protection similar to that obtained with acetylenic alcohols. 

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