Ketones Constitution

Many of the reactions assembled in Scheme 5.4are of undiminished interest in modern allene chemistry when relatively simple alkyl derivatives are the preparative goal. For example, /3-eliminations of enolphosphates prepared from saturated ketones constitute a simple route to 1,3-dialkylated allenes. Thus 3-octanone (49), on LDA treatment followed by quenching the generated enolate ions with diethyl chlor-ophosphate, affords a mixture of the enolphosphates 50. When these are treated with further LDA in THF at low temperatures, 2,3-octadiene (51) is produced in 50% yield (Scheme 5.5) [15]. 

All other cases of the pyran syntheses so far described involve one molecule of an ynamine as the acetylenic reactant. Simple [An + 27t] cycloaddition involving an ynamine and an a,j8-unsaturated aldehyde or ketone constitutes a general approach to N,N-disubstituted 6-amino-4//-pyrans 93 the stability and hence the yields depend on substituents R to R5 (Table... 

The acylation of unsaturated ketones constitutes one of the earliest routes to pyrylium salts (19CB1195). The reaction is better achieved with acyl halides than by anhydrides, and aliphatic are preferable to aromatic acid derivatives. The presence of a Lewis or Bronsted acid is usually necessary and iron(III) chloride, aluminum chloride, boron trifluoride and perchloric acid have found frequent application. It is considered that these interact with the acid derivative to generate the actual acylating agent. 

Pentyl-5 ( 2 ) -carbomethoxyoctyl-2-cyclopentenone and 2(5)-Hexyl-5 (2)-carbomethoxyheptyl-2-cyclopentenone (4). These cyclic ketones constitute about 35% (estimated by GLC) of the neutral diethyl ether extract of the salts and amount to 4.6% of the final reaction mixture of carboxylated linoleate. Analyses by GLC (JXR column) show one peak of retention time of 1.06 relative to that of 1 TLC (silica gel G, diethyl ether-petroleum ether, 1 3) Rf 3.74 compared with 5.04 for 2 IR (neat) 1740 (ester C=0), 1700 and 1630 cm"1 (C=C—C=0) UV max... 

Ketones constitute another important class that will yield radicals on irradiation. Nonconjugated ketones absorb weakly in the ultraviolet at 270 nm and decompose with cleavage at the carbonyl group as indicated in Equation 9.31. The carbonyl radical may then fragment further with loss of carbon monoxide according to Equation 9.32. Although this reaction can serve as a source of the... 

Aldehydes and ketones constitute an important class of organic compounds... 

Aldehyde or Ketone Compounds.—This aldehyde or ketone constitution is proven by several reactions. 

In discussing the aldehyde and ketone constitution of the monosaccharoses we stated that while this constitution holds for the compounds as they react in water solution it is not the constitution at present accepted for the actual substances themselves. 

Ketones constitute an important part of the volatile compounds. They represent 21.5% of the components of a coffee aroma (the center-cut of the fractionation, see in Alcohols, Section 5.B) described by Merritt et al. (1963), more than half being 2-butanone. 

The IMDA-Grob fragmentation strategy that starts with an allene cycloaddition reaction is illustrated in Scheme 43. The allene-furan cycloadduct was formed together with the other exoadduct which had the opposite configuration at the i-propyl group. Partial isomerization of the other product into the thermodynamic product shown and conversion into the 10-membered ketone constituted a formal synthesis of periplanone-B <88TL650l> since that ketone had been used in an... 

Another category of reductions involves aryl ketones. The Friedel-Crafts acylation reaction reacts benzene with an acid chloride such as butanoyl chloride (49) to give an aryl ketone, 50. Complete removal of the oxygen from this ketone constitutes a method to make straight-chain arenes, which cannot be prepared via Friedel-Crafts alkylation (see Section 21.3.2). At least two classical methods are used to accomplish this reaction, which is formally a reduction. If 50 is treated with zinc metal in HCl, the product is 1-phenylbutane, 105. This acidic reduction involves a mineral acid such as HCl and an active metal, and it is called the Clemmensen reduction. 

McMurry coupling of a,j5-unsaturated aldehydes and ketones constitutes an easy route to conjugated polyenes (Figure 6.2), which exhibit interesting electronic properties. After yS-carotene [3], a series of minicarotenes such as 11 has been syn-... 

Dehalogenation of oi,a dihaloalkenes and Ketones. The preparation (eq 24) of the iron carbonyl complex of trimethylen-emethane (42) and some Fc2(CO)9-mediated rearrangements of dibromo ketones constitute the pioneering work in this area. Noyori has extended the dehalogenation reaction of a-halo ketones to a,a -dibromo ketones and o,a,a, a -tetrabromo ketones which can be dehalogenated with Fe(CO)5 or Fe2(CO)9. ... 

The simple sugars or monosaccharides are polyhydroxy aldehydes or ketones, and belong to Solubility Group II. They are termed tetroses, pentoses, hexoses. etc. according to the number of carbon atoms in the long chain constituting the molecule, and aldoses or ketoses if they are aldehydes or ketones. Most of the monosaccharides that occur in nature are pentoses and hexoses. 

Finally a general approach to synthesize A -pyrrolines must be mentioned. This is tl acid-catalyzed (NH4CI or catalytic amounts of HBr) and thermally (150°C) induced tea rangement of cyclopropyl imines. These educts may be obtained from commercial cyan> acetate, cyclopropyl cyanide, or benzyl cyanide derivatives by the routes outlined below. Tl rearrangement is reminiscent of the rearrangement of 1-silyloxy-l-vinylcyclopropancs (p. 7 83) but since it is acid-catalyzed it occurs at much lower temperatures. A -Pyrrolines constitut reactive enamines and may be used in further addition reactions such as the Robinson anei lation with methyl vinyl ketone (R.V. Stevens, 1967, 1968, 1971). 

Hydrogen bonding m carboxylic acids raises their melting points and boiling points above those of comparably constituted alkanes alcohols aldehydes and ketones... 

Aldol Addition and Related Reactions. Procedures that involve the formation and subsequent reaction of anions derived from active methylene compounds constitute a very important and synthetically useful class of organic reactions. Perhaps the most common are those reactions in which the anion, usually called an enolate, is formed by removal of a proton from the carbon atom alpha to the carbonyl group. Addition of this enolate to another carbonyl of an aldehyde or ketone, followed by protonation, constitutes aldol addition, for example... 

Reactions 33 and 35 constitute the two principal reactions of alkyl hydroperoxides with metal complexes and are the most common pathway for catalysis of LPOs (2). Both manganese and cobalt are especially effective in these reactions. There is extensive evidence that the oxidation of intermediate ketones is enhanced by a manganese catalyst, probably through an enol mechanism (34,96,183—185). 

Tropic Acid. The constitution of both tropic and atropic acids is known from syntheses by Ladenburg et al. from acetophenone. The ketone (I) by treatment with phosphorus pentachloride was converted into a-dichloroethylbenzene (II), and this, by the action of potassium cyanide in alcohol, into ethoxycyanoethylbenzene (III), which on hydrolysis yielded ethylatrolactic acid (TV). The latter was converted by strong... 

KETONES OF THE MORPHINE GROUP. As these substances have played an important part in the discussion of constitutional formulae for the morphine group and the allied alkaloids, it is desirable to describe the more important of them. 

Constitution of Yohimbine and its Isomerides. The yohimb alkaloids are methyl esters of acids. Yohimbine, yohimbene, mesoyohimbine (isoyohimbine) and y-yohimbine (table, p. 502) are hydrolysed to four, distinct, monocarboxylic acids, C2,yH2402N2, each of which on decarboxylation by heating with soda-lime yields yohimbol, long supposed to be a secondary alcohol, Ci,yH240N2, but which Witkop has shown to be a ketone and has re-named yohimbone, C18H22ON2, m.p. 307° (dec.),... 

Morphine alkaloids, bimoleculat types, 255 Morphine sub-group, alkaloids, 213 constitution, 222 ketones, 245... 

The aldehyde or ketone is called the keto fonm, and the keto 5 enol equilibration referred to as keto-enol isomerism or keto-enol tatitomerism. Tautomers are constitutional isomers that equilibrate by migration of an atom or group, and theh equilibration is called tautomerism. The mechanism of keto-enol isomerism involves the sequence of proton transfers shown in Figure 9.6. 

Nitromifene (85) is such an agent. A Grignard reaction of aryl ether and ketone leads to tertiary carbinol Tosic acid dehydration leads to a mixture of 1 and stilbenes which constitute the antiestrogen, nitromi fene (85)... 

No aldehyde or ketone has been obtained from it by oxidation. Its constitution is probably allied to those of citronellol and rhodinol, but, since it contains an asymmetric carbon atom, as shown by its optical activity, the three formulae given under bupleurol obviously cannot represent androl. 

This ketone has been isolated from oil of rose, and in traces, from oil of cloves. It has the following constitution —... 

Irone is the odorous ketone present in oil of orris. It is isomeric with ionone, having the formula CJ3H2JO and the constitution—... 

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