A,fi -unsaturated carbonyl compounds

Michael addition of various a,fi-unsaturated carbonyl compounds to silyl enol ether catalyzed by Ti-beta and TS-1... 

The strong dependence of the reaction rate on the catalyst concentration relative to control experiments in which the amino-hydrogen atoms of 7 were substituted by methyl groups demonstrate that hydrogen bonding represents the major interaction responsible for the observed accelerations. Diels-Alder reactions are also accelerated by hydrogen-bond donors. It was shown that a biphenylenediol 9 is able to catalyse [4 + 2]-cycloadditions of cyclopentadiene, 2,3-dimethylbutadiene and other simple dienes with various a,fi-unsaturated carbonyl compounds (Table 14)175. 

Cyclopropanation of a,fi-unsaturated carbonyl compounds with dibromomalonates (typical procedure) To a mixture of diethyl dibromomalonate (0.95 g, 3 mmol) and methyl vinyl ketone (0.27 g, 3.1 mmol) is added dibutyl telluride (0.73 g, 3 mmol) under argon and with stirring. The exothermic reaction is completed within 1 h. The mixture is chromatographed on an AI2O3, column (70-230 mesh, elution with EtOAc), giving dibutyltellurium dibromide (1.01 g, 84%) and then l-acetyl-2,2-bis(ethoxycar-bonyl)cyclopropane, which is purified by Kiigelrohr distillation (0.59 g (86%) b.p. 88-90°C/0.08 torr). 

A review of photo-cycloadditions of dienones and quinones has been published.41 The first example of a Lewis acid-catalysed 2 + 2-cycloaddition of styrene with naphthoquinone has been reported.42 FMO methods have been used to investigate the effect of substituents on the regiochemistry of the 2 + 2-photo-cycloaddition of a, fi-unsaturated carbonyl compounds with substituted alkenes.43 Evidence has been presented for the presence of a triplet exciplex intermediate in the photo-cycloaddition of 4,4-dimethylcyclohexenone to 1,1-diphenylethylene.44 The intramolecular 2-1-2-photo-cycloaddition of 2-acyloxy-3-hexenoylcyclohexenones (26) is highly diastereo-selective yielding the tricyclic adduct (27) (Scheme 10).45... 

With sodium borohydride and catalytic amounts of titanyl acetoacetonate, a,fi-unsaturated carbonyl compounds give allyl alcohols regioselectively, whereas a-diketones and acyloins are reduced to vicinal diols.325 Enantioselectivities in the reduction of acetophenone, catalysed by 1,3,2-oxazaborolidones, have been examined using the AM1-SCF MO method. The optimized geometries, thermal enthalpies, and entropies of R and S transition states in the stereo-controlling steps of the reduction have been obtained.326... 

The reader is already familiar with the reductions of carbonyl compounds to alcohols, since they were described in Sections 10.2-10.4. (To complete the overall picture in a,fi-unsaturated carbonyl compounds the C=C- instead of the C=0 double bond can also be reduced according to Figure 13.20, through the Birch and L-Selectride reduction of such carbonyl compounds.)... 

Protocol 2 produces the protected fi-formylphosphonate 12 f)-ketophospho-nates may also be synthesized by other methods,23 however, they may not be prepared in unprotected form by the Michaelis-Arbuzov reaction because the Perkow reaction, in which an a-haloaldehyde or ketone and a trialkyl phosphite yield an enol phosphate (e.g. 13, Scheme 5,24 i.e. [P—O] bond formation), competes and frequently dominates (see Section 4). Conversely halocarboxylic acid derivatives (e.g. see Table 7.1, entry 3) and acyl halides (see Protocol 3) react well in the Michaelis-Arbuzov reaction to yield useful functionalized phosphonates. fi-Ketophosphonates are useful reagents for the synthesis of a,fi-unsaturated carbonyl compounds by the Horner-Wadsworth-Emmons reaction,3,4 25 and have other applications.23... 

Vinyl ether a,fi-Unsaturated carbonyl compound Temp. (°C) Conditions Time (h) Catalyst Yield... 

A Ca-positioned sulfoxide (as well as a sulfide) group enhances significantly the dienophilicity of a,fi-unsaturated carbonyl compounds in Diels-Alder reactions with standard dienes. Moreover, the synergistic influence of the two fiinctional groups secures a high regiochemical control, e.g. (75) + (76) (77)... 

Addition to enolizable carbonyl compounds 1.53.1.3 Stereocontrol in nucleophilic addition to carbonyl compounds 1.5.3.1.4 Addition to chiral alkoxycarbonyl compounds 1.5.3.13 Addition to a,fi-unsaturated carbonyl compounds... 

Common error alert a,fi-Unsaturated carbonyl compounds are not particularly acidic at the a-carbon atoms. The C=0 tt bond prefers to be in conjugation and coplanar with the C=C tt bond, so the C-H cr orbital does not overlap with the C=0 tt orbital. An unfavorable conformational change is required before deprotonation of the a-carbon can even begin. Note that the low acidity of a,(3-unsatu-rated carbonyl compounds as compared with their saturated congeners contradicts the general rule that C(sp2) is more acidic than C(sp3), all else being equal. 

Selective reduction of a,fi-unsaturated carbonyl compounds. Japanese chemists1 have reported selective reduction of ot,/(-unsaturated carbonyl compounds in the terpene field by use of triethylsilane and the rhodium(I) complex as catalyst. Thus... 

Reduction of a,fi unsaturated carbonyl compounds. The following example is taken from Emil Fischer s classical Anieitung, the first laboratory manual for beginning students. 

The attachment of a,fi-unsaturated carbonyl compounds to polymeric supports via silyl-enol ether has been employed in some combinatorial libraries. Thus, a,(3-unsaturated lactones (316, 321) can be enolized by KHMDS, then trapped by polystyrene-bound silylchlorides (315) [311]. The resulting furans (317, 322) reacted with methylacrylate to give only endo adducts (319, 323) (Scheme 67). 

Scheme 12.11. Intermolecular addition to a,fi-unsaturated carbonyl compounds.

Dimethyl sulfoxide-Sulfur trioxide [1, 309, before references]. The combination of DMSO and sulfur trioxide, in the form of the pyridine complex, in the presence of trimethylamine oxidizes primary and secondary alcohols in good yield to aldehydes and ketones, respectively.55 The reaction usually is complete within minutes and the products are isolated by acidification and precipitation with water. The reagent also oxidizes allylic alcohols to the corresponding a,fi-unsaturated carbonyl compounds. One advantage over the DMSO-DCC method is that the elaborate purification required when dicyclohexylurea is a product can be dispensed with. Testosterone, with a 17/3-hydroxyl group, was oxidized toA -androstene-3,17-dione very rapidly the 17-epimer required a period of 35 min. 

Alkali Metal Enolates by Addition to a,fi-Unsaturated Carbonyl Compounds... 

Catalytic hydrogenation of a,fi-unsaturated carbonyl compounds. a,0-Unsaturated aldehydes and ketones are reduced to the corresponding saturated carbonyl compounds with high selectivity under conditions of the oxo reaction [H2,CO,Co2(CO)a, 1,225-226]. ... 

Among the most unusual aspects of lycoctonine chemistry is the intriguing transformation of the lactam (184) to an a,fi -unsaturated carbonyl compound, designated as lycoctamone, by vigorous treatment with acid. In... 

Cyclocondensation of phenols with a, fi-unsaturated carbonyl compounds Chromene formation is catalyzed by base, aldehydes are favoured as cyclocondensation components. 

In Conjugate Monoorganocopper Addition to a,fi-Unsaturated Carbonyl Compounds. TMSI has been demonstrated to efficiently promote the reaction of conjugate 1,4-additions of monoorganocopper compounds into a... 

We shall discuss ways of disconnecting this starting material, and other a,fi-unsaturated carbonyl compounds, later in the chapter. 

The aldol reaction is a classical method for the creation of C-C bonds in organic synthesis [41]. Reductive aldol reaction of a,fi-unsaturated carbonyl compounds with saturated carbonyl compounds promoted by catalytic amounts of various... 

---