A,j3-unsaturated ketone

Me3SiSCH2CH2SSiMe3, Znl2, Et20, 0-25°, 12-24 h, high yields. Less hindered ketones can be selectively protected in the presence of more hindered ketones. a,j3-Unsaturated ketones are selectively protected (94 1, 94 4) in the presence of saturated ketones by this reagent. ... 

HSCH2CH2SH, Zn(OTf)2 or Mg(OTf)2, CICH2CH2CI, heat, 16 h, 85-99% yield.Excellent selectivity can be achieved between a hindered and an unhindered ketone. a,j3-Unsaturated ketones such as carvone are not cleanly converted to ketals, because of Michael addition of the thiol. 

Cyclic 1,3-diacetoxy-l,3-dienes can be generated in situ from cyclic 1,3-diketones under the influence of isopropenyl acetate. The dienes then undergo Diels-Alder reactions with maleic anhydride giving as products 1-acetoxybicycloalkane dicarboxylic anhydride derivatives (10). The procedure is also successful with cyclic 1,2- and 1,4-diketones as well as cyclic a,j3-unsaturated ketones. The products, after hydrolysis to... 

Wiles, C., Watts, P., Haswell, S. J., Pombo-Villae, E., 1,4-Addition of enolates to a,j3-unsaturated ketones within a micro reactor. Lab. Chip 2 (2002)... 

The addition of thiols to a,j3-unsaturated ketones with [bmim][PF ] in water was investigated. It was found that product could be obtained in up to 95% yield in 10 min (Scheme 77) [199]. 

The 3-oxo derivatives (515) have been prepared by the reaction of hydroxyurea with some a,j3-unsaturated ketones (75TL2979). 

Thermolysis of the tosylhydrazones of a,j3-unsaturated ketones in the presence of alkoxide ion was found to give cyclopropenes99 or 3H-... 

It is possible to monitor the reaction and determine the end point by the absence of an a,j3-unsaturated ketone absorption in the UV or by the determination of the consumption of ca. one molar equivalent of hydrogen peroxide by permanganate titration.568... 

It may comfort you to know that most a,j3-unsaturated ketones will do conjugate addition if the enol(ate) equivalent is carefully chosen. 

In aprotic solvents, an increase in solvent polarity resulted in an increase in the amount of ds-0-decalone formed. Similar results were also obtained in the hydrogenation of cholestenone and testosterone (see Table I). If, as suggested by McQuillin et al. (3), a more polar aprotic solvent will facilitate complexation of the carbonyl oxygen of an a,j3-unsaturated ketonic system in the same way that it increases its polarization (25), it can be assumed that what is occurring in these polar solvents is a 1,4-addition of hydrogen to the conjugated system. 

Beyond the scope discussed so far, Michael additions also include additions of stoichiometrically generated enolates of ketones, SAMP or RAMP hydrazones, or esters to the C=C double bond of a,j3-unsaturated ketones and a,/3-unsaturated esters. These Michael additions convert one kind of enolate into another. The driving force stems from the C—C bond formation, not from differential stabilities of the enolates. It is important that the addition of the preformed enolate to the Michael acceptor is faster than the addition of the resulting enolate to another... 

Under appropriate experimental conditions, hydrogen telluride, phenyl tellurol, and sodium hydrogen telluride perform the selective reduction of double bonds of a,/3-unsaturated carbonyl systems.89 90 This reaction with a,j3-unsaturated ketones complements the cerium trichloride/sodium borohydride method, which reduces the carbonyl group, keeping the carbon-carbon double bond intact92 (Scheme 18). 

The reaction of an organometallic reagent with an a,j3-unsaturated ketone can occur by 1,2-addition to the carbonyl group and by 1,4-... 

The nucleophile adds to the a,J3-unsaturated ketone electrophile in a Michael reaction to generate a new enolate as product. r H3C H H ... 

Since the a,j3-unsaturated ketone CXLIV was converted to conessine previously (94) the total s3mthesis of latifoline also constitutes a formal total synthesis of conessine. 

We examined optically active pyrrolidine derivatives as efficient chiral catalysts in the asymmetric 1,4-addition of thiols to a,j3-unsaturated ketones. Thus, benzenethiol in the presence of 1 mol% of a chiral diamino alcohol, 3a-f, as catalyst was added to 2-cyclohexen-l-one in toluene at —20 °C. The results are listed in Table IS . 

The Stereochemistry of Hydrogenation of a,j3-Unsaturated Ketones Robert L. Augustine... 

These cyclization reactions were also possible with or without a metal ion template using a,j3-unsaturated ketones, such as mesityl oxide or methyl vinyl ketone, or with /3-hydroxyketones, such as 4-hydroxy-4-methyl-2-pentanone. The products were the same as when simple carbonyl compounds were used showing that the reaction with the simple carbonyl compounds proceded... 

Base-catalyzed reactions of amino sugars with 2,4-pentanedione in a nonaqueous solvent (piperidine-triethylamine-methanol) have also been reported. The products obtained under these conditions from 2-amino-2-deoxy-D-glucose are 3-acetyl-2-methyl-5-(D-ami)OTo-tetrahydroxybutyl)-pyrrole (2) (in about 90% yield) and 2-deoxy-2-n(4-oxopent-2-enyl)-amino]-D-glucose (28). Proofs that structure (28) is correct were (a) the ultraviolet absorption, typical of a -amino a,j3-unsaturated ketone, (b) a positive test with the ferric chloride reagent, and (c) quantitative... 

In any conformationally mobile a,j3-unsaturated ketone that exists as a mixture of s-cis and s-trans isomers at room temperature there will usually be one conformer that will be energetically more favourable. It is therefore to be expected that a decrease in temperature will increase the population of the favoured isomer, and this may be detectable in the benzene-induced solvent shifts of the substituents. Variable-temperature studies in toluene-c g solution of some model fixed s-m and s-trans a,) -unsaturated ketones have been carried out and the data for 3-methyl-cyclohexenone (33) are fairly typical (see Fig. 4 the chemical shift is given in c./sec. at 100 Me./sec. relative to internal TMS). 

Addition of aldehydes to activated double bonds. Aldehydes add to a,j3-unsaturated ketones, esters, and nitriles in the presence of triethylamine and catalytic amounts of this salt. Other thiazolium salts are effective. 

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