O ,/! unsaturated

The Michael reaction is of central importance here. This reaction is a vinylogous aldol addition, and most facts, which have been discussed in section 1.10, also apply here the reaction is catalyzed by acids and by bases, and it may be made regioselective by the choice of appropriate enol derivatives. Stereoselectivity is also observed in reactions with cyclic educts. An important difference to the aldol addition is, that the Michael addition is usually less prone to sterical hindrance. This is evidenced by the two examples given below, in which cyclic 1,3-diketones add to o, -unsaturated carbonyl compounds (K. Hiroi, 1975 H, Smith, 1964). 

F E R R I E R Chiral cyclohexanone synthesis Transtormatlon o< unsaturated glycosides into cyclohexanone derivatives by heating in aqueous acetone with mercury (II) salts... 

MEYER - SCHUSTER Propargyl alcohol rearrangement Add catalyzed rearrangement of acetylenic alcohols into o, -unsaturated carbonyl derivatives... 

Michael addition of aromatic or heterocyclic aldehydes (via cyanohydrins) to o. unsaturated systems. Also addilion of aliphatic aldehydes catalyzed by thiazoFium yKds... 

The solvent for ammonia may have an important influence. In reduction of C,o unsaturated dinitriles to primary amines over ruthenium-on-alumina, ammonia-/-butanol proved the preferred system normal alcohols gave poor rates and secondary alcohols produced N-alkylated products 18). 

The choice of the desired CM-partner directly influences the choice of the catalyst [147], Comparing the GII and the HII catalysts shows that the latter has access to a much broader spectrum of cross-partners [148], It is possible to use electron deficient cross-partners like acroleine, perfluorinated olefins, acrylonitrile, or other o / -unsaturated carbonyls, whereas GII leads to no reaction or very low conversions due to side-reactions in these cases. 

The vinylcyclopropane 144, bearing two electron-withdrawing groups, undergoes the intermolecular palladium-catalyzed [3 + 2]cycloaddition reaction of the Jt-allylpalladium intermediate 145 with o, -unsaturated esters or ketones to provide a useful method for forming the cyclopentane ring of 146 [74]. (Scheme 51)... 

Kosjek, B., Tellers, D.M., Biba, M., Farr, R. and Moore, J.C., Biocatalytic and chemocatalytic approaches to the highly stereoselective 1,2-reduction of an o ,/ -unsaturated ketone. 

A synthetic method for the preparation of the diketone substrates has been presented HiU, C.L., McGrath, M., Hunt, T. and Grogan, G., A generic and reproducible route to homo- and heteroannular bicyclic /3-drketones via Knochel-type 1,4-conjugate additions to o ,/ -unsaturated cycloalkenones. Synlett, 2006, 309. 

An unexpected endo selectivity in addition of certain carbon and sulfur nucleophiles to the O, / -unsaturated (arene)ruthenium(II)cyclopentadienyl compound (154) has been reported. This stereochemistry has been compared with that of the 5 n2 reactions but a detailed theoretical approach is yet to be undertaken. ... 

The epoxidations of propylene and isobutylene with peroxyformic acid proceed in a concerted way via slightly unsymmetrical Markovnikov-type transition stmctnres where the differences in the bond distances between the donble-bond carbons and the spiro oxygen are only 0.021 and 0.044 A at the QCISD/6-31G level. In contrast, the more polarizable natnre of the carbon-carbon double bond of o ,/ -unsaturated systems results in a highly nnsymmetrical transition structure for the epoxidation of 1,3-butadiene with an order-of-magnitnde difference in the carbon-oxygen bond distances of 0.305 A at the QCISD/6-31G level. A highly unsymmetrical transition structure has been also found for the epoxidation of acrylonitrile. 

Epoxidations of methyl-snbstituted alkenes and o ,/ -unsaturated systems as 1,3-bntadiene and acrylonitrile with peroxyformic acid follow a concerted asynchronous pathway. 

Type IV (spectators to CM) 1,1-Disubstituted olefms " 1,1-Disubstituted olefms, disub. o ,/ -unsaturated carbonyls, 4° allylic carbon-containing olefins, perfluorinated alkane olefins, 3° allylamines (protected)" Vinyl nitro olefins, protected trisubstituted allyl alcohols, a,/ -olefin of 2-subst. 1.3- butadienes, a,/ -olefm of electronically deactivated 1.3- butadienes ... 

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible 101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[l03,104], NaBhp is also used for the Pd-catalyzed reduction of nitro compounds 105], However, the o ,/ -unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]. 

The first successful approaches were based on the, often Cu-mediated, conjugate addition of organolithium and organomagnesium (Grignard) reagents to o ,/ -unsaturated systems covalently modified with chiral auxiliaries (Scheme 1 ). ... 

Iodolactonization of y, o-unsaturated alcohols results in preferential formation of tram-2, 5-disubstituted tetrahydrofuranes. However, the corresponding benzyl ethers cyclize preferentially to the cis-isomers. The alkyl group must be bulky enough to exert a steric effect, but not to prevent cyclization. Substituted benzyl ethers are particularly useful. Examples of this steric control are illustrated for the preparation of tram- and c/s-linalyl oxide (equations I and II).10... 

The presence of two electrophilic reaction centers in the molecule of o -unsaturated carbonyls is responsible for their ability to participate in the synthesis of heterocycles. Such compounds can react as ambident electrophiles owing to delocalization of electron density in a C=C-C=0 system. The addition of nucleophiles to these molecules can proceed in one of two main directions—via attack of the carbonyl group (1,2-addition) or involving the / -carbon (1,4-addition). 

Tlie use of aqueous NaOH results in the isolation of a 0-hydroxy ketone provided the alcohol is not a substituted benzyl alcohol. The alcohol can be heated with add or I3 to yield the o -unsaturated carbonyl molecule. In cases wliere the initially formed alcohol is a derivative of benzyl alcohol, a molecule of H,C is lost spontaneously. 

The photochemistry of o< -unsaturated ketones has attracted much attention and is still a field fiettd of current interest. /Numerous examples of such photochemical transformations are well-documented for cyclic enones and dienones, including both cycloaddition reactions and rearrangements. For example, cyclopentenones 1 and 2 readily rearrange to... 

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