Unsaturated compounds enones

Convenient disconnection of the 1,5-dicarbonyl pattern results in the a,p unsaturated compound, enone, with a highly reactive C=C bond. Partners in the synthesis are neutral enone and a-carbanion of the second carbonylic reagent to complete the well-known Michael addition [22, 23]. Hence, the disconnection of the central bond in the 1,5-dicarbonyl pattern is denoted as the retro-Michael. 

Addition of Organometallic Reagents to Enones in Aqueous Media Rhodium-catalyzed 1,4-addition of organometallic reagents to a,p-unsaturated compounds was first developed by Miyaura in 1997. Thus, Rh(acac)(CO)2/dppb was found to catalyze the 1,4-addition of aryl- and alkenylboronic acids to several ot,(3-unsaturated ketones in water-containing solvents at 50°C. The reaction conditions were successfully modified for the development of an asymmetric variant of this process by Hayashi and Miyaura in 1998. The important points of modification are (1) the use of Rh(acac)(C2H4)2/(5)-binap as a catalyst and... 

A new tandem Michael-aldol reaction of a,ft-unsaturated compounds bearing a chalcogenide or thioamide group with electrophiles has been reviewed.163 The product o -(o -hydroxyalkyl)enones - Morita-Baylis-Hillman (MBH) adducts - can be formed with significant stereocontrol when an optically active thione is used. 

Thus activation and functionalization of alkenes, enones and conjugated dienes are possible based on the 7i-allylpalladium complex formation from these unsaturated compounds. 

The problem of getting direct (1,2-) or conjugate (1,4- or Michael) addition to ct, 3-unsaturated compounds such as enones 11 can be solved without finding abstruse strategies by choice of reagents. 

Selenenyl halides are relatively stable, though moisture sensitive, compounds that are generally prepared by the reactions shown in Scheme 7 and behave as electrophihc selenium species. " They react with ketones and aldehydes via their enols or enolates to afford a-seleno derivatives (e.g. (17) in equation 11). Similar a-selenenylations of /3-dicarbonyl compounds, esters, and lactones can be performed, although the latter two types of compounds require prior formation of their enolates. Moreover, the a-selenenylation of anions stabilized by nitrile, nifro, sulfone, or various types of phosphorus substituents has also been reported (equation 12). In many such cases, the selenenylation step is followed by oxidation to the selenoxide and spontaneous syn elimination to provide a convenient method for the preparation of the corresponding a ,/3-unsaturated compound (e.g. 18 in equation 11). Enones react with benzeneselenenyl chloride (PhSeCl) and pyridine to afford a-phenylselenoenones (equation 13). 

For the transfer of arj l and alkenyl groups to enones, Hayashi s procedure, employing the corresponding boronic adds and a rhodium-BINAP catalyst, is the method of choice at present [24, 25]. For the transfer of alkyl groups to cydic enones the use of dialkylzinc reagents in the presence of copper-phosphoramidite catalysts is superior. Although the first examples of hi ly enantiosdective 1,4-ad-ditions of R Zn reagents to nitroalkenes have been reported, similar catalytic methods for numerous other dasses of a, -unsaturated compounds still need to be devdoped. 

The Michael reaction of silyl enol ethers with a,P-unsaturated ketones (enones) has generally been performed with the aid of a stoichiometric amount of Lewis acid to afford 1,5-dicarbonyl compounds 80,81). When the reaction was conducted thermally in acetonitrile (82), under high pressure (Si), or by the catalytic use of (Me2N)3S MesSiFj" (84) or Ph3C CI04 (S5), the intermediate adducts were isolable in the form of synthetically valuable silyl enol ethers. 

When saturated alkyl halides were used in place of allyl compounds, a zinc/cop-per couple or zinc dust/copper iodide promoted the 1,4-addition to a-enones or a-enals. Sonication enhanced the efficiency of the process leading to the 1,4-adducts in very good yields [166]. This reaction was later extended to various a,j3-unsaturated compounds such as esters, amides and nitriles [167]. The reactivity of the halide followed the order tertiary > secondary primary and iodide > bromide > chloride making the assumption of a radical process highly probable [168]. 

Oxidation of unsaturated compounds. Methyl ketones are produced from 1-aIkenes using molecular oxygen as oxidant [catalyst Pd(OAc)2-pyridine]. On the other hand, methyl 3,3-dimethoxypropanoate is formed when eth l acrylate is oxidized on activated carbon-supported molybdovanadophosphate and Pd(OAc>2 in acidic ethanol. Treatment of enones with LiAlH4 under dry oxygen gives 1,3-diols. ... 

Isomerizations of Unsaturated Compounds. r-BuOK is an effective base for bringing about migrations of double bonds in alkenes and alkynes via carbanion intermediates, but since the base promotes these reactions most effectively in DMSO, they will be described in more detail under Potassium tert-Butoxide-Dimethyl Sulfoxide. Important exanples of enone deconjugations with i-BuOK/f-BuOH which proceed via di- and trieno-late intermediates are shown in eqs 30 and 31. Potassium i-pentoxide is effective in promoting the latter reaction, but various lithium amide bases are not, apparently because they de-protonate the enone at the a -position regioselectively. The isomerization of Q ,/8-unsaturated imines to alkenyl imines (eq 32) is an important step in an alternative method for reduction-alkylation of a ,/8-unsaturated ketones. ... 

Other Unsaturated Compounds. - The dienals 13 (with D-xylo-, D-lyxo- and D-arahino-configurations) have been condensed with the phosphonate 14 to give the enone adducts 15 the intramolecular Diels-Alder reactions of these adducts are mentioned in Chapter 22. Treatment of the unsaturated lactone 16 with the Tebbe reagent has afforded 17 its conversion into a cyclooctene derivative is covered in Chapter 18. Exposure of the cyclic sulfate 18 to base has afforded a mixture of the exo- and endo-olefins 19 and 20, ° and a syn-selective dihydroxyla-tion of the 3,4-unsaturated pyranoside 21 generated predominantly the D-allo product. Synthesis of the branched-chain 5,6-ene 22 using standard methods, and its conversion into a cyclitol during the first total synthesis of (—)-tetracyc-line is mentioned in Chapter 22. 

Pore et al. (2006) documented the thia-Michael addition involving the conjugate addition of thiols to a,p-unsaturated ketones in the presence of SSA as a heterogeneous catalyst under solvent-free conditions at room temperature (Scheme 5.53). The catalytic activity was comparatively studied with potassium phosphate. Studies revealed that SSA is suitable for electron-deficient a,P-unsaturated compounds, whereas K3PO4 catalyzed the reactions of both electron-deficient as well as electron-rich enones. SSA catalyzes a rapid, green, and chemoselective aza-Michael addition of amines and thiols... 

Electron-deficient unsaturated compounds other than enones also undergo conjugate addition of organocopper reagents. Synthesis of cyano ester (CCLIII) and dimethylcuprate (Sobti and Dev, 1967, 1970). 

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