Unsaturated ketones conjugated

The addition of active methylene compounds (ethyl malonate, ethyl aoeto-acetate, ethyl plienylacetate, nltromethane, acrylonitrile, etc.) to the aP-double bond of a conjugated unsaturated ketone, ester or nitrile In the presence of a basic catalyst (sodium ethoxide, piperidine, diethylamiiie, etc.) is known as the Michael reaction or Michael addition. The reaction may be illustrated by the addition of ethyl malonate to ethyl fumarate in the presence of sodium ethoxide hydrolysis and decarboxylation of the addendum (ethyl propane-1 1 2 3-tetracarboxylate) yields trlcarballylic acid ... 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

Data collected on the uv spectra of steroids are available in several books, spectmm adases, and review articles (263). The most characteristic absorptions in steroid hormones include a,P-unsaturated ketones, conjugated dienes, and phenoHc A-rings (264). 

The only other functional group is the conjugated unsaturated ester. This functionality is remote from the stereocenters and the ketone functionality, and does not play a key role in most of the reported syntheses. Most of the syntheses use cyclic starting materials. Those in Schemes 13.4 and 13.5 lead back to a para-substituted aromatic ether. The syntheses in Schemes 13.7 and 13.8 begin with an accessible terpene intermediate. The syntheses in Schemes 13.10 and 13.11 start with cyclohexenone. Scheme 13.3 presents a retrosynthetic analysis leading to the key intermediates used for the syntheses in... 

Unsaturated ketones of all kinds can be converted to saturated ketones, to unsaturated alcohols, to saturated alcohols, to alkenes and to alkanes. If the double bond is conjugated with the carbonyl group reduction usually takes place more readily and may give, in addition to the above products, e-diketones formed by coupling at j -carbons. 

Reduction of unsaturated ketones to unsaturated alcohols is best carried out Nit v complex hydrides. a,/3-Unsaturated ketones may suifer reduction even at the conjugated double bond [764, 879]. Usually only the carbonyl group is reduced, especially if the inverse technique is applied. Such reductions are accomplished in high yields with lithium aluminum hydride [879, 880, 881, 882], with lithium trimethoxyaluminum hydride [764], with alane [879], with diisobutylalane [883], with lithium butylborohydride [884], with sodium boro-hydride [75/], with sodium cyanoborohydride [780, 885] with 9-borabicyclo [3.3.1]nonane (9-BBN) [764] and with isopropyl alcohol and aluminum isopro-... 

With saturated, or non-conjugated unsaturated, cyclic ketones, a-cleavage takes place readily in solution on irradiation, usually in a triplet-stale process. The resulting acyl-alkyl btradicals have a num-... 

Photochemical enolization of conjugated unsaturated ketones is particularly important in the photochemical rearrangements of the ionones. a-Ionone (Formula 172) gives two products, cts-a-ionone (Formula 173)... 

The photochemical rearrangements of saturated ketones are initiated by n - ir excitation of the carbonyl group. It is interesting to contrast the photochemical rearrangements of conjugated unsaturated ketones (which are also initiated by n — ir excitation) with the reactions of saturated ketones. 

The first step is a condensation of the aldol type (see Section 5.18.2, p. 799) involving the nucleophilic addition of the carbanion derived from the methyl ketone to the carbonyl-carbon of the aromatic aldehyde. Dehydration of the hydroxyketone to form the conjugated unsaturated carbonyl compound occurs spontaneously. 

Resonance is more important in a,j8-unsaturated ketones. Conjugation of the carbonyl group with the carbon-carbon double bond increases opportunities for electron delocalization. 

Presumably the silyl enol ether of 37 adds in a conjugate fashion to the unsaturated ester 39 and the intermediate enolate then cyclises onto the cation 40 to give 38. This will happen only if the stereochemistry of 40 is the same as that of the product 38 as the 4/5 and 4/6 ring fusions must both be cis. This suggests that the first step is reversible. The formation of the cyclobutane requires that particular relationship between ketone and unsaturated ester so this kind of reaction is less versatile than photochemical cyclisation. Asymmetric versions of these reactions are also known.14 Probably the most versatile thermal method to make cyclobutanes uses ketenes and is the subject of the next chapter. 

The seven-membered metallacycles 89 (formed by ketone addition to [(butadiene)ZrCp2] cleanly add a nitrile molecule at elevated temperatures to yield the respective nine-membered metallacyclic products 96. Their hydrolysis then yields the 6-hydroxy-substituted non-conjugated unsaturated imines 97 under kinetic control. Within a few hours at room temperature these rearrange to the thermodynamically favored primary dienamine products 98.107 In this case the thermochemical diene conjugational energy makes the primary dienamines more stable than their conjugated imine tautomers (Scheme 32). 

The first step is probably the addition of hydrogen peroxide to the C—C double bond, since conjugated unsaturated ketones are very difficult to ketalize.49 The intermediate hydroperoxyketone (49)... 

When KHSO4 was replaced by 75% phosphoric acid, the corresponding non-conjugated unsaturated ketone was obtained as illustrated in Eq. 2 described below. 

Reynolds (19) has given a preliminary report of experiments which show that persulphate resembles periodate In oxidising the l 2-glycol groups of which there are about 2% In polyvinyl alcohol although the reaction Is not quantitative. Conjugated unsaturated ketone groups axa also formed these may retard polymerisation. 

Intramolecular hydrogen-transfer to a nearby free-radical is a general phenomenon (see Chapter 10) and in a diradical (13) can, in principle, occur in either of the two ways depicted, to give either (a) a non-conjugated unsaturated aldehyde (14), or (b) a ketene (15). In the C-nor-ketone 12) hydrogen transfer... 

Conjugated unsaturated ketones are unreactive to peracids because of the depletion of electronic charge in the olefiinic bond, but epoxyketones are readily prepared by using the nucleophilic hydroperoxide ion (H02"") [284], In simple aliphatic compounds the epoxidation follows kinetics first order with respect to hydroperoxide ion and unsaturated ketone [28s]- According to House [286], the reaction should be represented as a reversible addition of hydroperoxide ion, followed by closure of the epoxide ring in a slow step, with expulsion of hydroxide ion. The over-all rate will be determined both by the equilibrium constant in the first step and by the rate constant for the second. 

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