Olefinations ketones

Because of their relative instabiUty, primary phosphine oxides caimot be isolated and must be converted direcdy to derivatives. Primary and secondary phosphine oxides undergo reactions characteristic of the presence of P—H bonds, eg, the base-cataly2ed nucleophilic addition to unsaturated compounds such as olefins, ketones, and isocyanates (95). 

Hydroboration affords an efficient preparation of the 5a-A -system (141, for example) from A" -3-ketones. Reaction with diborane followed by decomposition of the organoboron intermediate with refluxing acetic anhydride gives good yields of olefins. Ketones must be protected, and alcohols are transformed to acetates. A -7-Ketones yield 5oc-A -olefins (for example, 138). 

Olefinketon, n, olefinic ketone, olefin ketone, Olein-saure,/, oleic acid, -saureseife, -seife,/. olein soap, red-oil soap, -schmdlze,/, (Tea> tiles) olein softener, olein emulsion, olen, v.t. oil lubricate, grease. 

Compounds containing double-bonded silicon and germanium atoms are the nearest analogues of olefins, ketones and thioketones. However, most of them are very unstable and highly reactive species. 

This chapter discusses the development of scaleable and robust manufacturing processes for rhodium and rathenium containing precatalysts that are used for the asymmetric hydrogenation of a diverse range of olefins, ketones and imines. The application of these precatalysts to the preparation of a variety of pharmacentical intermediates, many of which have been operated on commercial scale, is also discussed. 

Addition of alkyllithium to cyclobutanones and transmetallation with VO(OEt)Cl2 is considered to give a similar alkoxide intermediates, which are converted to either the y-chloroketones 239 or the olefinic ketone 240 depending on the substituent of cyclobutanones. Deprotonation of the cationic species, formed by further oxidation of the radical intermediate, leads to 240. The oxovanadium compound also induces tandem nucleophilic addition of silyl enol ethers and oxidative ring-opening transformation to produce 6-chloro-l,3-diketones and 2-tetrahydrofurylidene ketones. (Scheme 95)... 

The development of chiral phosphorus ligands has made undoubtedly significant impact on the asymmetric hydrogenation. Transition metal catalysts with efficient chiral phosphorus ligands have enabled the synthesis of a variety of chiral products from prochiral olefins, ketones, and imines in a very efficient manner, and many practical hydrogenation processes have been exploited in industry for the synthesis of chiral drugs and fine chemicals. 

Similarly, high stereoselectivity has also been observed in acetylenic ketone or olefinic ketone reductions (Scheme 6-25). 

As noted above, titanocene-alkylidenes can be prepared using various methods and starting materials. Like the methylidene complex, higher alkylidene complexes are useful for the transformation of carbonyl compounds to highly substituted olefins. Ketones and aldehydes are converted into substituted allenes by treatment with titanocene-alkenylidenes prepared by olefin metathesis between titanocene-methylidene and substituted allenes (see Scheme 14.7) [17]. Titanocene-alkenylidene complexes can also be prepared from... 

Fig. 16. Proposed reaction mechanism for the olefin ketonation and epoxidation catalyzed by platinum-blues.

Reductive cyclizations of nonconjugated olefinic ketones (see Scheme 8) [12] or... 

Indeed, in many cases the creation of soluble nanoparhcles has provided singular catalyhc activities/selectivities that differ from those expected for both molecular (single-site) and heterogeneous (mulh-site) catalysts [40, 41]. As a result, iridium nanoparticles have attracted much interest in terms of their catalyhc performance in the hydrogenation of olefins, ketones and aromahc compounds. 

Catalytic asymmetric reduction of unsaturated compounds is one of the most reliable methods used to synthsize the corresponding chiral saturated products. Chiral transition metal complexes repeatedly activate an organic or inorganic hydride source, and transfer the hydride to olefins, ketones, or imines from one... 

Asymmetric catalytic hydrogenation is unquestionably one of the most significant transformations for academic and industrial-scale synthesis. The development of tunable chiral phosphorous ligands, and of their ability to control enantioselectivity and reactivity, has allowed asymmetric catalytic hydrogenation to become a reaction of unparalleled versatility and synthetic utility. This is exemplified in the ability to prepare en-antiomerically enriched intermediates from prochiral olefins, ketones, and imines through asymmetric hydrogenation, which has been exploited in industry for the synthesis of enantiomerically enriched drugs and fine chemicals. 

Some studies seeking preferred conditions for this reaction have been made. Optimum yields are obtained when the amount of water present is appreciable, and it was noted that the rate of hydrogen evolution increases with increasing water content. A 75% formic acid system appears generally preferred. Under the reaction conditions examined by the submitters, olefins, ketones, esters, amides, and acids are inert, but nitro compounds are reduced to the formamide derivative. 

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