A,fS-enones

An endo-selective ionic Diels-Alder reaction of a,/f-enone and a,/f-enal acetals catalyzed by electrogenerated acid [99]... 

Ni-Gr 2.2 Semihydrogenation of triple bonds proceeds more slowly and with somewhat less stereoselectivity with Ni-Gr 2 than with Ni-Gr 1. Ni-Gr 2 is particularly useful as a catalyst for hydrogenation of a,/f-enones and /1-diketones. 

Tricarbonyliron complexes of enones.1 Reaction of Fe2(CO), with a,f -enones in toluene at 70-75° results in tricarbonyliron complexes, which on reaction with Grignard reagents, organolithium, or organocuprates are converted into 1,4-diketones. 

Lithium salts of y8-diketones and regioisomeric yfi-aminovinylketones, /1-aminovinylthiones, a,/f-enones, and their halogen derivatives are being actively... 

Khomutov et al. developed effective universal methods for the syntheses of 3-fluoroalkyl-2-aziridinylketones from fluorine-containing a,/f-enones (94IZV282) (Scheme 124). 

An exploration of structural modifications on the activity of prolinol catalysts has been published <06T12264>. More electron-rich aromatic rings on the prolinol scaffold improve the activity in the epoxidation of a, 3-enones. The reaction of 10 with an enone and f-BuOOH provides the epoxy-ketones with moderate levels of enantioselectivity. 

E. J. Corey, F.-Y. Zhang, Mechanism and Conditions for Highly Enantioselective Epoxidation of a,p-Enones Using Charge-Accelerated Catalysis by a Rigid Quaternary Ammonium Salt , Org. Lett. 1999,1,1287-1290. 

OrPhenybelenenylation of a,f -unsaturated esters.3 (F)-3r,/MJnsaturated esters are converted to a-phenylseleno-a,0-unsaturated esters in 20-65% yield by reaction with LDA followed by C6H5SeBr. The reaction is related to the reaction of a,/ -enones with pyridine and C H5SeCl (9, 28-29), and is also believed to involve conjugate addition of the base followed by selenenylation of the enolate. 

The Stille coupling of a-iodo enones is sluggish under standard conditions. Significant rate enhancement was observed for the Stille reaction of 2-chloro-5-tributylstannylpyridine and a-iodo enone 76 using triphenylarsine as the soft palladium ligand and Cul as the co-catalyst [63]. Oxygenated functionalities did not affect the efficiency of the reaction provided both Ph3As and Cul were added. Additional manipulations of 77 resulted in the synthesis of (-f)-epibatidine (78). 

This sequence can be used for conversion of a simple /Tsilyl-a,/J-enone such as 1 into a more substituted a,/f-unsaturated enone, as shown in equation (II). 

Cacchi, S. Fabrizi, G. Gasparrini, F. Pace, P. Villani, C. The utilization of supercritical C02 in the Pd-catalyzed hydroarylation of /i-substi-tuted-a,/i-enones. Synlett 2000, 650-652. Amorese, A. Arcadi, A. Bemocchi, E. Cacchi, S. Cerrini, S. Fedeli, W. Ortar, G. Conjugate addition vs vinylic substitution in Pd-catalyzed reaction of aryl halides with /i-substituted-a, /i-enones and -enals. Tetrahedron 1989, 45, 813-828. 

The Michael addition of nitroalkanes to a,f -unsaturated enones, catalysed by the novel chiral imidazolidine-2-yltetrazole (151), has been investigated. The new, more soluble organocatalyst decreases reaction times and improves enantioselectivities com- pared with other catalysts. The Michael addition adducts were obtained with up to 92% ee.179... 

AUylic oxidation.1 Reaction of alkenes with f-butyl hydroperoxide (90%) in the presence of catalytic amounts of Cr(CO)6 results in oxidation to a,p-enones in 25-100%... 

The reagent forms the expected adducts with aldehydes and ketones in high yield. It can be used for preparation of f-butoxymethyl ketones from acid chlorides (equation I). In combination with CuBr, it undergoes conjugate addition to a,(3-enones (equation II). 

Other reagents have been utilized for this transformatian. For exanqile, lead tetiabenzoate (with fluoride-induced hydrolysis of (136) and (137).However, success is restricted to acyclic ketones. Where cyclic dienol ethers are employed, products derived from a-oxidation are obtained. 

Baeyer- Villiger reaction the oxidation of a ketone to an ester or lactone, nsnally by means of a peroxy acid Enone an unsaturated ketone, usually a, f relative to the carbonyl group... 

Kinetic resolution is operative in the reaction with 4-substituted cyclopent-2-en-l-ones. For instance, when 2 equiv. of racemic 4-(l-methyl-l-phenylethoxy)-2-cyclopentenone (79) is reacted with the carb-anion (78), (5)-(79) reacts to yield predominantly the product derived by approach of the caibanion from the si face of (79). The formation of the cis adduct probably results from the chelation of lithium counterion with the C-4 oxygen (equation 22). Kinetically selective resolution of a bicyclic enone (80) is also effected. treatment of the carbanion of (/f)-(78) with racemic (80) (2 equiv.), an enantiomer of (82) and (5)-(80) are obtained in 80% and 45% yields respectively. Addition of the lithio derivative (2 equiv.) of... 

Reductions. Hydrogen teUuride reduces aldehydes and ketones to alcohols in satisfactory yields. The combination Al2Te3-D20 permits deuteration. H2Te reduces a,/i-enones and a,/f-enals to the saturated carbonyl compound.1... 

Intramolecular aldol condensations. Swiss chemists have reported two examples of preparation of cyclic aldols by reaction of f-oxo-a,j3-enones by conjugate addition of dimethylcopperlithium followed by a directed intramolecular aldol condensation. Both aldols are products of kinetic control they are not... 

Scheme 3.82 Conventional and modern routes for conversion of a,f -unsaturated cyclic enones to a-substituted cyclic ketones.

Alfonsi M, Arcadi A, Aschi M, Bianchi G, Marinelli F (2005) Gold-catalyzed reactions of 2-alkynyl-phenylamines with a,p-enones. J Org Chem 70 2265-2273. doi 10.1021/jo047793i... 

Corey EJ, Zhang F. Enantioselective Michael addition of nitromethane to a,(3-enones catalyzed by chiral quaternary ammonium salts. A simple synthesis of (R)-baclofen. Org. Lett. 2000 2(26) 4257 259. 

In 2005, Lattanzi et al. reported a series of a,a-diphenyl-L-prolinols 442 for the enantioselective epoxidation of different a,p-enones. The epoxides have been obtained in good yields and with up to 80% ee [298]. Further investigations were carried out in order to improve the enantioselectivities. On the one hand the substi-tntion pattern of the phenyl residne was tuned and on the other hand the size of the cyclic amine was modified. In these studies, the catalysts 442e-f proved to be more effective compared to other a,a-aryl-prolinols and secondary cyclic P-amino alcohols 443 and 444 (Table 7.30) [299, 303, 304]. 

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