B-Unsaturated ketones

Addition of Carbanions to a B Unsaturated Ketones The Michael Reaction... 

However, the two methods of choice for the oxidations of a, (B-unsaturated ketones are based on lanthanoid-BINOL complexes or a biomimetic process based on the use of polyamino acids as catalysts for the oxidation 1"1. 

The most useful method synthetically involves treatment of the substrate with at least two equivalent of an organolithium compound (MeLi) in ether, hexane, or tetramethylenediamine. Tosylhydrazones of a, b-unsaturated ketones give conjugated dienes. 

In 1978, Saegusa and coworkers discovered that silyl enol ethers can be converted into a,b-unsaturated ketones and aldehydes by Pd" [193]. In the presence of 0.5 equivalents of BQ, substoichiometric Pd(OAc)2 (0.5 equiv) effects nearly quantitative conversion of the substrate into product in acetonitrile (Eq. 51). Attempts to lower the catalyst loading further results in longer reaction times as well as increased yields of saturated carbonyl by-product. 

Addition-elimination mechanisms. In the reaction between a,B-unsaturated ketones and alkaline peroxide (5-36), the oxidizing agent adds to the substrate and then part of it is lost ... 

In contrast, to the difficulty of ring closure by the 5-Endo-Trig pathways, the 6-Endo-Trig reaction occurs readily on treatment with methanolic sodium methoxide the 0, B-unsaturated ketones 186 smoothly closed to the 4-chroma-nones 1187) (56). 

In conclusion, in the case of 1,4-conjugated additions to a,B-unsaturated ketones, some substrates, in order to avoid steric interaction, react through a boat conformation to give an equatorially substituted product, but when there is no steric interaction, the axial attack through a chair conformation is energetically favored. Both processes are however stereoelectroni-cally controlled. 

The photocycloaddition of (cyclic) a,(B-unsaturated ketones to alkenes affording cyclobutanes as products comprises the four reaction types shown in Sch. 1, i.e., (a) intermolecular enone + alkene cycloaddition (b) cycloisomerization of alkenylsubstituted enones (c) photocyclodimerization of enones, one ground state enone molecule acting as alkene and (d) cycloisomerization of fe-enones. 

Henry and Michael-Henry addition of nitroalkanes to aldehydes, alicyclic ketones and a,B-unsaturated ketones were performed at r.t. with TMG 3 as catalyst moderate then good [3 a] yields were obtained in direct and conjugated addition products. ... 

Cyclohexenone is a cyclic a,B-unsaturated ketone whose carbonyl IR absorption occurs at 1685 cm-1. If direct addition product A is formed, the carbonyl absorption will vanish and a hydroxyl absorption will appear at 3300 cm"1. If conjugate addition produces B, the carbonyl absorption will shift to 1715 cm-1, where 6-membered-ring saturated ketones absorb. 

The enolate of 3-cyclohexenone can be protonated at three different positions. Protonation at the y position yields the a,B-unsaturated ketone. 

Placement of an sp carbon at either the a- or B-carbon atoms should not alter the internal angle strain however, it does generate a markedly different chromophore (i.e., an a,B-unsaturated ketone). 

The excited states involved in the mechanisms of the photochemical transformations of the 2-alkylidenecyclo-butanones were elucidated without special difficulty (vide supra). These a, B-unsaturated ketones undergo only one of the reactions characteristic of cyclobutanones (i.e., ring expansion). In addition, the triplet energy of the enone chromophore is low enough that this excited state may be efficiently and selectively populated by standard carbonyl triplet sensitizers (e.g., acetophenone, xanthone, and benzophenone), thereby demonstrating that ring expansion occurs via the 2-alkylidenecyclobutanone state, while the isomerization process (i.e., [81]J[82]) occurs via T. ... 

Low reactivity of ot,(B-unsaturated ketones and sterically hindered ketones as well as separation of reaction products from phosphine oxide are a few disadvantages of the classical Wittig reaction. Phosphonate anions are stronger nucleophiles than related phosphoranes thus, alkenate hindered ketones under mild conditions. The dialkylphosphate (R2PO4), the other product of the HWE reaction, can easily be removed from the reaction mixture because it is soluble in water. 

On the one hand, thioacetals of a,B-unsaturated ketones resulting from the a-alkylation reaction reported above have been transformed efficiently into the corresponding unsaturated ketones on reaction with mercury(II) chloride and oxide in methanol (Scheme 71, entry or on reaction - with... 

The studies of MeAlCh-induced cyclization of unsaturated ketones indicate the advantage of alkylaluminum chloride over AlCI in Lewis acid catalyzed reactions, since these reagents are capable of acting as proton scavengers as well as Lewis acids [33]. The reaction is interpreted as a MeAlCL-promoted cyclization of the y,b-unsaturated ketone followed by the sequential hydride and methyl shift as illustrated below. 

COPPER-CATALYZED CONJUGATE ADDITION OF FUNCTIONALIZED ORGANOZINC REAGENTS TO a.B-UNSATURATED KETONES ETHYL 5-(3-OXOCYCLOHEXYL)PENTANOATE... 

Selective reduction of the carbonyl group of benzylideneacetone has been achieved with an iridium catalyst (Scheme 2).11 This represents the first highly selective catalytic hydrogenation of the carbonyl group of an a,B-unsaturated ketone. 

In the reaction of aqueous NaCN with an a,B unsaturated ketone like... 

Stereoelectronic effects should also play an important role in the nucleophilic 1,4-additions of anions to conjugated systems. These effects should therefore influence the Michael reaction as well as the hydrocyanation of o,B-unsaturated ketones. Studies on these reactions provided evidence that the kinetically controlled addition of a nucleophile to a cyclohexenone derivative is indeed subject to stereoelectronic effects. 

In Scheme 3, the a-bromoketones XVIII and XIX were converted to lactones XXIII and XXIV by refluxing in collidine (4.16.38). By-products of this reaction include the a, B-unsaturated ketone XXV Which results from the dehydrobromlnation (M, ) of XVIII. Ketone XXVI results from a one-step dehydrobromlnatlon-decarbomethoxylatlon ( -43) of XIX. 

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