Mesityl oxide, conjugate addition

V,7V-dimethylaminopyridme provides l-(2-methoxycarbonyl)ethoxy- (40,69%) and l-(2-methoxycarbonyl-l-methyl)ethoxytryptamine (41, 72%), respectively (Scheme 4). The conjugate addition to mesityl oxide proceeds successfully as well, giving iVb-acetyl-1-(1, l-dimethyl-3-oxo)butoxytryptamine (42,49%), while the reaction with methyl 3-methylcrotonate affords 43 in a miserable yield (1.6%). Addition to acrolein results in failure, and 44 is not yet obtained. 

In addition to conjugated dienes, cyanocobalt catalysts also hydrogenate the C=C bond of activated alkenes.52 Carvene, mesityl oxide, 2-cyclohexenone, benzalacetone and an androstenone derivative were reduced in this way.53... 

Dimedone has a trivial name because its preparation is so easy that it was discovered early in the history of organic chemistry. The first step is a conjugate addition of diethyl malonate to the unsaturated ketone mesityl oxide (4-methylpent-3-en-2-one given a trivial name for the same reason). Ethoxide ion is the base for the usual reason that nucleophilic substitution at the ester group simply regenerates starting material. 

The aldol reaction in carbonyl compounds has its equivalents in 7i-electron deficient heterocycles. In the carbanion approach, lithiated acetophenone added rapidly and regioselectively to 1-substituted 2-pyrimidinones to form the 3,4-dihydro isomer (279) (Scheme 45) <85ACS(B)195>. The adducts are readily oxidized to their aromatic equivalents (280) by DDQ. With the lithium enolate of mesityl oxide, however, equal amounts of the two dihydro isomers were formed <88JOM(338)34l>. In highly 7i-electron deficient heterocyclic systems, aldol reactions will also take place under the influence of acid catalysis such as in the addition of acetone to the pyrimidinone (281) the product is fully conjugated (282) after DDQ dehydrogenation <79ACS(B)150>. 

Reaction of e/7mesityl oxide proceeds with high stereoselectivity to give an endo adduct (Whitesides and Kendall, 1972). Stereoselectivity in the conjugate addition of cuprates to 2-cyclo-hexenone, including octalones, has been examined in detail (Marshall et al., 1966 Marshall and Roebke, 1968 House and Fischer, 1968). 

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