Olefinic ketones reduction

Catalytic processes based on the use of electrogenerated nickel(O) bipyridine complexes have been a prominent theme in the laboratories of Nedelec, Perichon, and Troupel some of the more recent work has involved the following (1) cross-coupling of aryl halides with ethyl chloroacetate [143], with activated olefins [144], and with activated alkyl halides [145], (2) coupling of organic halides with carbon monoxide to form ketones [146], (3) coupling of a-chloroketones with aryl halides to give O -arylated ketones [147], and (4) formation of ketones via reduction of a mixture of a benzyl or alkyl halide with a metal carbonyl [148]. 

Titanium-catalyzed cyclization/hydrosilylation of 6-hepten-2-one was proposed to occur via / -migratory insertion of the G=G bond into the titanium-carbon bond of the 77 -ketone olefin complex c/iatr-lj to form titanacycle cis-ll] (Scheme 16). cr-Bond metathesis of the Ti-O bond of cis- iij with the Si-H bond of the silane followed by G-H reductive elimination would release the silylated cyclopentanol and regenerate the Ti(0) catalyst. Under stoichiometric conditions, each of the steps that converts the enone to the titanacycle is reversible, leading to selective formation of the more stable m-fused metallacycle." For this reason, the diastereoselective cyclization of 6-hepten-2-one under catalytic conditions was proposed to occur via non-selective, reversible formation of 77 -ketotitanium olefin complexes chair-1) and boat-1), followed by preferential cyclization of chair-1) to form cis-11) (Scheme 16). 

The discovery by the recent Nobel-laureate, Ryoji Noyori, of asymmetric hydrogenation of simple ketones to alcohols catalyzed by raras-RuCl2[(S)-binap][(S,S)-dpen] (binap = [l,l -binaphthalene-2,2/-diyl-bis(diphenylphosphane)] dpen = diphenylethylenediamine) is remarkable in several respects (91). The reaction is quantitative within hours, gives enantiomeric excesses (ee) up to 99%, shows high chemoselecti-vity for carbonyl over olefin reduction, and the substrate-to-catalyst ratio is >100,000. Moreover, the non-classical metal-ligand bifunctional catalytic cycle is mechanistically novel and involves heterolytic... 

This section contains dehydrogenations to form olefins and unsaturated ketones, esters, and amides. It also includes the conversion of aromatic rings to olefins. Reduction of aryls to dienes is found in Section 377 (Olefin-Olefin). Hydrogenation of aryls to alkanes and dehydrogenations to form aryls are included in Section 74 (Alkyls, Methylenes, and Aryls from Olefins). 

PET reaction of carbonyl compounds with olefins form either oxetanes (Paterno-Buchi reaction, Eq. 31) by direct coupling or a radical pair reaction leading to coupling product or reduction. The carbonyl-olefin radical pairs are formed by proton transfer within their radical ion pairs (Eq.32). Both these aspects of ketone-olefin photoreaction have been recently rationalized by Mattay et al. [167] from the photoreactions of 2,3-butanedione (208) with different olefins such as 209 and 210 as shown in Scheme 39. Photoprocesses of... 

Rh and Ir complexes stabilized by tertiary (chiral) phosphorus ligands are the most active and the most versatile catalysts. Although standard hydrogenations of olefins, ketones and reductive aminations are best performed using heterogeneous catalysts (see above), homogeneous catalysis becomes the method of choice once selectivity is called for. An example is the chemoselective hydrogenation of a,/ -unsaturated aldehydes which is a severe test for the selectivity of catalysts. 

Another popular olefination-reduction sequence starts with commercially available ketone 122, transformed into olefin 123 using a Wittig or Wittig-Horner reaction [103] (illustrated in Scheme 11.32). Reduction of the double bond proceeds with high stereocontrol to yield the alio derivative 124. The cis arrangement at C2-C3 allowed formation of lactone 125 and the synthesis of avenaciolide 126 [104,105]. 

Other reductions. A limitation to the reductions cited is that the reagent can react with other organic functions such as the carbonyl group of aldehydes and ketones, olefinic and acetylenic unsaturation. - ... 

Similarly Ni catalysts are useful substitutes to Pd for the selective olefin reduction in an a,/8-unsaturated ketone. Finely divided Ni (and partially deactivated by washing it with a 0.1% MeOH solution of acetic acid) in a mixture 5% HCCl3/EtOH is efficient at RT and atm P. Neutral catalysts, U—Ni—N, obtained by refluxing precipitated Ni with isopropanol, also shows selectivity, mesityl oxide being reduced to methyl-1 pentanone-2 . 4-Cyclopentene-l,3-dione, 5, can be converted into 1,3-cyclo-pentanedione, 6, by hydrogenation over partially deactivated neutral Ni catalyst ... 

The intramolecular reductive ketone-olefin coupling was realized by Molan-der et al. by the combination SmI2/THF-f-BuOH [126]. For example, the spiro-... 

Another class of chelation-controlled reactions involves Sml2, which has been used to mediate inter- and intramolecular ketone-olefin couplings [17], Matsuda and collaborators showed that coupling erpt/ira-) -hydroxyketone with acrylonitrile led exclusively to the anti diol under Sml2 reductive conditions [18]. Chelation control model J in Scheme 6 was proposed to account for the sense of diastereo-selectivity. In this model, chelation of the Smb to both the jff-hydroxy and the... 

Nevertheless, it must be pointed out that the formation of such transient species has never been spectroscopically observed. Native CDs are effective inverse phase-transfer catalysts for the deoxygenation of allylic alcohols, epoxydation,or oxidation " of olefins, reduction of a,/ -unsaturated acids,a-keto ester,conjugated dienes,or aryl alkyl ketones.Interestingly, chemically modified CDs like the partially 0-methylated CDs show a better catalytic activity than native CDs in numerous reactions such as the Wacker oxidation,hydrogenation of aldehydes,Suzuki cross-coupling reaction, hydroformylation, " or hydrocarboxylation of olefins. Methylated /3-CDs were also used successfully to perform substrate-selective reactions in a two-phase system. 

A number of derivatives of compound A were prepared that included acetates, ethers, olefin reduction products, aldehyde and ketone reduction products, aromatic decarbonylated derivatives, and derivatives where the aldehyde was converted to a methyl ester [122]. 

Wilkinson s catalyst is frequently used to hydrogenate olefins in the presence of additional functional groups. The selectivity for olefin reduction in the presence of esters, ketones, and nitroarenes, and for reduction in the absence of olefin isomerization make this catalyst superior in many cases to heterogeneous catalysts. A few of the early applications of this catalyst are presented here. 

Carbonylation. Dialkylchloroboranes have also been used in the preparation of asymmetric ketones via reduction-hydroboration-carbonylaton protocol. In the presence of 1.0 equiv of trimethyl silane, IpcBCl2 is reduced to IpcBHCl, which selectively hydroborates terminal olefins faster than internal olehns, furnishing the dialkyl chloroborane. Upon further reduction of the R2BCI with LiAlH4, the internal olefin undergoes hydrobora-... 

Later improvements addressing both problems of limited solubility and hydrolytic stability came with the development of water-soluble ligands having the notable DuPHOS skeleton, for which excellent enantioselectivity in ketone, olefin and imine reductions have been reported. Zhang and RajanBabu groups independently pursued the synthesis... 

Phenylthio)methyl]carbinyl benzoate esters, e.g. (34), easily prepared from ketones, undergo reductive elimination to give high yields of olefins, e.g. (35) on treatment with titanium metal in refluxing THF (Scheme 12). ... 

The next task was to convert 42 to ketone 44. This transformation called for a regioselective hydration of the C13-C14 olefin. This was accomplished by vicinal dihydroxylation of the olelin, which was accompanied by formation of the y-lactone (rather that the d lactone). The preference for y-lactonization (which is most often the case in such simations) left the C14 hydroxyl group free for oxidation to ketone 43. Reductive cleavage of the a-C-O bond, and esterification of the resulting acid, gave 44 (see 99 to 100 in Alkaloids-12 for comparison). 

Low-valent nitrogen and phosphorus compounds are used to remove hetero atoms from organic compounds. Important examples are the Wolff-Kishner type reduction of ketones to hydrocarbons (R.L. Augustine, 1968 D. Todd, 1948 R.O. Hutchins, 1973B) and Barton s olefin synthesis (p. 35) both using hydrazine derivatives. 

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