Conjugate addition reactions Alumina

Iodine-Mercury(II) oxide, 149 Lithium diisopropylamide-Potassium /-butoxide, 164 Molybdenum carbonyl, 194 Phenyliodine(III) diacetate, 242 Sulfuryl chloride, 284 Conjugate addition reactions Michael reactions Alumina, 14... 

Alternatively, Ballini devised a new strategy to synthesize tri-alkylated pyrroles from 2,5-dialkylfurans and nitroalkanes <00SL391>. This method involves initial oxidation of 2,5-dimethylfuran with magnesium monoperoxyphthalate to cA-3-hexen-2,5-dione (6). Conjugate addition of the nitronate anion derived from the nitro compound 7 to 6 followed by chemoselective hydrogenation of the C-C double bond of the resulting enones 8 (obtained by elimination of nitrous acid from the Michael adduct) completes the conversion to the alkylated y-diketones 9. Final cyclization to pyrroles 10 featured improved Paal-Knorr reaction conditions involving reaction of the diketones with primary amines in a bed of basic alumina in the absence of solvent. 

Conjugate addition of RN02 to enones. Primary nitroalkanes and a, (3-enones when activated by alumina form conjugate addition products that are oxidized in situ by alkaline hydrogen peroxide to 1,4-diketones. A similar reaction of nitromethane with a vinyl ketone provides 1,4,7-triketones. 

Michael reaction with exocycHc ,(S-enones Conjugate addition of secondary amines to a,/ -enones proceeds readily unless the enonc is cxocyclic. in "Such a case the reaction is very slow unless alumina is added as catalyst. Thus the reaction of 1 and diethylamine in the presence of alumina proceeds in 2 hours to give 2 quantitatively. 

High yields of hydroxythioxanthones are readily obtained with good regioselectivity when a mixture of alumina and methanesulfonic acid is used to effect the reaction between thiosalicylic acid and phenols <04S2900> and a one-pot conjugate addition - aldol reaction sequence provides benzo[6]thioxanthene-6,l 1-diones from naphthoquinone and 2-acylthiophenols (Scheme 24) <04BCJ2095>. 

Among the various derivatives of biomass, furan compounds obtained from furfural are important (200 000 t year ). A new family of furan diethers has been obtained by alkylation of 2,5-furandimethanol or furfuryl alcohol under the action of microwave irradiation with PTC solvent-free conditions (Scheme 10.79) [154]. Reaction times were improved by use of microwave irradiation, and the same conditions were extrapolated to the synthesis of a series of new furan diethers by alkylation of furfuryl alcohol by dihalides. 1,4-Diketones substituted by furans or thiophenes were synthesized by conjugate addition of aldehydes to a,j8-unsaturated ketones by irradiation without solvent in the presence of thiazolium halides and DBU adsorbed on alumina [155]. 

The amine-immobilized silica-alumina catalyst achieved a good yield of 2-cyano-5-oxo-2-(3-oxobutyl) hexanoic acid ethyl ester from the Michael reaction between nitrile and a,P-unsaturated ketone (Table 7.6). Notably, the reaction using a mixture of triethylamine and unfunctionahzed sihca-alumina gave a lower yield than the amine-immobilized silica-alumina, and both triethylamine and silica-alumina were inactive alone for the reaction. In general, the conjugate addition of nitrile compounds to a,P-unsaturated ketones requires strong base or transition metal... 

The addition of hydrogen cyanide (HCN) to carbon-carbon double bonds activated by electron-withdrawing groups in the presence of a base as a catalyst (a variation of the Michael Reaction) has been known for a long time. Nitriles were also obtained by hydrocyanation of branched olefins, such as isobutylene and trimethylethylene, in vapor phase reactions in particular the reactions over alumina (3) and cobalt-on-alumina (4) were reported in the late 1940s and early 1950s. Addition of HCN to conjugated dienes in the presence of cuprous salts (vapor and liquid phase) was reported as early as 1947 (5). 

The addition of iodine azide to double bonds gives p-iodo azides. The reagent can be prepared in situ from KI—NaNa in the presence of Oxone -wet alumina. The addition is stereospecific and anti, suggesting that the mechanism involves a cyclic iodonium ion intermediate. The reaction has been performed on many double-bond compounds, including allenes and a,p-unsaturated ketones. Similar reactions can be performed with BrNa and CfNa. 1,4-Addition has been found with acyclic conjugated dienes. In the case of BrNa, both electrophilic and free-radical mechanisms are important, whUe with CIN3 the addi-... 

Here a surface Lewis acid (denoted by j) abstracts a hydride ion from the methylene group adjacent to the double bond. This mechanism is in accord with the essential Lewis acid nature of the silica-alumina surface and is consistent with the previously demonstrated ability of this surface to abstract hydride ions from tertiary hydrocarbons. Since an alkenyl carbonium ion is stabilized by resonance to a greater extent than is a saturated carbonium ion, it may well be the most stable species which could form in the chemisorption of an aliphatic olefin or its precursor. It seems reasonable, therefore, to presume that such species may be involved in heterogeneous acid catalysis to a greater extent than has been generally recognized. This chemisorption process does not, of course, exclude the more conventional acid addition to the double bond which may occur under suitable circumstances but rather, it introduces an alternate path which may well exert a considerable influence on the overall course of catalytic reactions. Thus, for example, since a substituted ally lie carbonium ion may be converted to a conjugated diene by loss of a proton, it may be an important intermediate in the formation... 

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