Ketones unconjugated unsaturated

Unconjugated unsaturated aldehydes and ketones can be reduced without affecting the carbonyl group, particularly with a Pd catalyst Ni and Pt have been used, but the reduction must be terminated after the addition of 1 equiv. of hydrogen. The nitrile group also can survive the reduction of carbon-carbon unsaturation in the same molecule. 

The use of copper chromite at 40°C and atmospheric pressure was not very effective for selective carbonyl group hydrogenation. Unsaturated alcohols were produced from unsaturated aldehydes in low yields at low conversions and not at all from methyl vinyl ketone. 28 With unconjugated, unsaturated aldehydes, copper chromite is effective as a selective hydrogenation catalyst. Hydrogenation of 46 at 140°-160°C and 200 atmospheres gave better than 70% of the diene diol, 47. Increasing the temperature to 240°C resulted in the complete saturation of 46 (Eqn. 18.28). 29... 

Although selective hydrogenation of the carbonyl group of a,P-unsaturated ketones does not appear possible at this time, the keto group can be selectively hydrogenated with unconjugated, unsaturated ketones provided the... 

Isophorone usually contains 2—5% of the isomer P-isophorone [471-01-2] (3,5,5-trimethyl-3-cyclohexen-l-one). The term a-isophorone is sometimes used ia referring to the a,P-unsaturated ketone, whereas P-isophorone connotes the unconjugated derivative. P-lsophorone (bp 186°C) is lower boiling than isophorone and can be converted to isophorone by distilling at reduced pressure ia the presence of -toluenesulfonic acid (188). Isophorone can be converted to P-isophorone by treatment with adipic acid (189) or H on(Ill) acetylacetoate (190). P-lsophorone can also be prepared from 4-bromoisophorone by reduction with chromous acetate (191). P-lsophorone can be used as an iatermediate ia the synthesis of carotenoids (192). 

Table 8.17 shows the scope of the reaction of acetylcobalt tetracarbonyl with polyenes. The reactions are regiospecific with the acetyl group adding to the terminal unsaturated carbon atom of the ir-electron system to produce the E-a,p-unsaturated ketones [9]. In the reaction with fulvenes [10], only the 1-acetyl and 1,4-diacetyl derivatives are formed, with no evidence of the 2-isomer. This is an indication of the relative stabilities of the cyclic it-allyl complexes, compared with the exocyclic complex. It has been postulated that, in the reactions of conjugated systems, the initial o-allyl adduct proceeds to the products via the it-allyl complex (cf Scheme 8.1), whereas in the case of unconjugated tt-systems, the initial o-adduct is more stable and tends to undergo a further carbonylation reaction. 

In the carbonylation of unconjugated dienes the nature of the products is influenced by reaction conditions. With Pd halides in ethanol at 100°C and 97 atm CO, 1,5-cyclooctadiene is successively carbonylated to the unsaturated monoester and then to the saturated diester (II). With (Ph3P)2PdCl2 in ethanol-HCl and 300-700 atm CO, the monoester is produced selectively at 60°C and the diester at 100°C (8). Finally, with (Bu3P)2PdI2 in THF at 150°C and 1000 atm CO, 1,5-cyclooctadiene undergoes transannular addition of CO to give a cyclic ketone in 40-45% yield (14, 15). The mechanism proposed involves a a-7r-cyclooctenyl... 

Mixed chromophores with both C=C and C=0 moieties such as ,/3-unsaturated enones are one of the most investigated chromophores in organic photochemistry. Conjugation of the two chromophoric moieties results in lowering the n —> ji and tt ji energy levels relative to the unconjugated chromophores. UV absorption spectra of selected alkenes, ketones and enones are presented in Table 1. 

For the synthesis of tris-annulated benzene rings, the aldol trimerization of cyclic ketones has been known as a powerful tool since the 19 century. Why the reaction works so well with some ketones (e.g., indanone) but fails so miserably with others (e.g., tetralone), however, has never been adequately explained. This chapter outlines the development and scrutiny of a hypothesis that says formation of an a,/ -unsaturated (conjugated) dimer from a cyclic ketone is vital to the success of an aldol trimerization reaction for the synthesis of a tris-annulated benzene the reaction will fail with ketones that form only / ,y-unsaturated (unconjugated) dimers. This hypothesis unifies much experimental chemistry and is supported by theoretical calculations. 

Two simple a, P-unsaturated acylsilanes, l-trimethylsilyl-2-propen-l-one (III) and l-trimethylsilyl-2-methyl-2-propen-l-one (IV) were chosen for polymerization studies. The polymerization of the carbon analogues of these a,p-unsaturated acylsilanes, that is, 4,4-dimethyl-2-propen-3-one (vinyl tert-butyl ketone, V) and 2,4,4-trimethyl-2-propen-3-one (isopropenyl tert-hutyl ketone, VI) has been studied by Willson et al. 16, IT), These authors reported that whereas V readily polymerizes under free-radical-polymerization conditions, VI undergoes polymerization only under anionic-initiation conditions in the presence of a crown ether as a complexing reagent. On the basis of UV and NMR spectroscopic data, Willson et al. (i6, 17) ascribed the difference in polymerization behavior to the nonplanar, unconjugated structure of ketone VI brought about by steric hindrance caused by the methyl group at C-2. 

Unsaturated ketones have been prepared in moderate yield through the acylation of ir-allylnickel complexes with activated 2-pyridyl carboxylates. But, isomerization of the initially formed unconjugated alkene resulted in mixtures of products and limited the value of the method. Substituted ir-allylnickel complexes derived from crotyl bromide or cinnamyl bromide were acylated in 79% and 50% yields, respectively, without formation of the a,3-unsaturated ketone. ... 

The synthesis of /3,7-unsaturated ketones is often complicated by a tendency toward rearrangement to produce mixtures of conjugated and unconjugated ketones. The use of dry cerium(m) chloride allowed the regiocontrolled addition of organolithium to enaminones (Scheme 308). 

The term a-isophorone is sometimes used in referring to the a,jS-unsaturated ketone, whereas j6-isophorone connotes the unconjugated derivatives [1,2]. Isophorone is produced by aldol condensation (trimerization) of acetone under alkaline conditions. Severe reaction conditions effect the condensation and partial dehydration of three molecules of acetone. Both liquid and vapor phase continuous technologies are practiced... 

The first step in this transform comprises formation of a radical dianion (1-2) from reaction of at the sites of lowest electron density (Scheme 4.1). In the case of steroids, this requirement rules out all but positions 1,4 of the aromatic ring A. The charges on the intermediate then strip protons from the alcohol in the reaction medium to yield the dihydrobenzene 1-3. The alcohol, frequently tert-butanol, thus acts as a quench. The enol ether function in the product is sufficiently robust to serve as a protecting group in many subsequent reactions. Mild acid hydrolysis of that enol ether affords the surprisingly stable unconjugated ketone 1-4. Treatment of this last intermediate with mineral acid causes the unsaturation to move over into conjugation at C4 (1-5). 

The reduced reactivity of o(,j3-unsaturated ketones towards 3-mercapto-ethanol allows preferential formation of the hemithioacetal of an unconjugated carbonyl present in the molecule. One example of this general... 

Conjugated unsaturated aldehydes and ketones are more stable than their unconjugated isomers... 

---