Ketones, cyclic, conjugated

Reduction of conjugated carbonyl compounds using stoichiometric amounts of the ammonium salt shows little advantage over the sodium salt in acidic methanol [11] with both reagents producing allylic alcohols (58-88% for acyclic compounds and 15-64% for cyclic compounds) by selective 1,2-reduction of the conjugated systems. Aldehydes, ketones and conjugated enones are also reduced by tetra-n-butylammonium cyanoborohydride in HMPA [11, 12], whereas haloalkanes and alkanesulphonic esters are cleaved reductively under similar conditions [13]. 

Kekule structure org chem A molecular structure of a cyclic conjugated system that is depicted with alternating single and double bonds. ka-k3,la. strak-char j ketal oRG CHEM 1. Former term for the =CO group, as in dimethyl ketal (acetone). 2. Any of the ketone acetates from condensation of alkyl orthoformates with ketones in the presence of alcohols. ke,tal ... 

Compound A is a cyclic, nonconjugated keto alkene whose carbonyl infrared absorption should occur at 1715 cm-. Compound B is an a,B-unsaturated, cyclic ketone additional conjugation with the phenyl ring should lower its IR absorption below 1685 cm-1. Because the actual IR absorption occurs at 1670 cm-1, B is the correct structure. 

The enantioselective reduction of cyclic conjugated enones may be best accomplished using a complex of LAH with (11) to which EAP has been added.Optimum conditions for these reductions involve treatment of the ketone with 3 equiv of a 1 1 2 complex of LAH-(—)-(ll)-EAP in ether at —78 °C for 3 h (Table 3). However, under these conditions, acetophenone is reduced to the (R)-alcohol in only 54% ee. 

The exact position of the carbonyl absorption often provides additional information about a compound. For example, most aldehydes have a C=0 peak around 1730 cm , whereas for ketones, it is typically around 1715 cm . Two other structural features—ring size (for cyclic ketones) and conjugation—affect the location of the carbonyl absorption in a predictable manner. 

An interesting variation in this reaction combined an intermolecular Mukaiyama aldol followed by an intramolecular reaction (a domino Mukaiyama aldol) that gave cyclic conjugated ketone products.Borane derivatives such as C=C—OB(NMe2)2 react with aldehydes to give p-amino ketones. ... 

MCD measurements are useful not only in purely spectroscopic investigations, for example, in the detection of hidden absorption bands or for the identification of degenerate absorptions, but also in structural organic chemistry. There is, for instance, a rule that describes the influence of the molecular environment on the MCD effect of the n- r band of a ketone (Seamans et al., 1977 Linder et al., 1977). However, the method is clearly most useful for investigating cyclic conjugated n systems. 

Table 16. Enones and Other Products from the Photorearrangements of Cyclic Conjugated Cyclopropyl Ketones...

In a single step aUcynones ate transformed into cyclic conjugated ketones. This reaction does not go through hydration. 

KETONE, CONJUGATE ALLYLATION OF a,g-UNSATURATEO. 62, 86 KETONE, a-TERT-AUYLATION, 62. 95 Ketones, a,6-acetylen1c, asymnetrlc reduction, 63, 63 Ketones, cyclic, lactams from, 63, 188 Ketones, e-hydroxy-, synthesis of, 63, 79... 

Corey and Estreicher have developed the first method for the transformation of cyclic ketones into conjugated cyclic nitro-olefins. Following conversion of the ketone into a vinylstannane via its trisyl hydrazone, the crucial step is the replacement of tin by a nitro-group at the unsaturated carbon, for which tetranitromethane in DMSO is highly effective (e.g. Scheme 36). 

Two useful carbonyl group transpositions involve the intermediacy of sulphur compounds. In the first, the dithioacetal (131) is metallated (Bu"Li 4 eq.) and hydrolysed to the ketone (132), whereas Scheme 22 shows a sequence for the regiospecific transposition of cyclic conjugated enones. ... 

An electrochemical counterpart to this cyclization is provided by the anodic reduction of non-conjugated olefinic ketones cyclic tertiary alcohols are formed (Scheme 101) in a process initiated by electron addition to the carbonyl group. This method is limited to cases leading to formation of five-and six-membered rings it provides some interesting stereochemical results, e.g, the isolation of cw-l,2-dimethylcyclopentan-l-ol, whereas methyl-magnesium iodide on 2-methylcyclopentanone gives mainly the trans-di-methyl isomer. 

The 3.8-nonadienoate 91, obtained by dimerization-carbonylation, has been converted into several natural products. The synthesis of brevicomin is described in Chapter 3, Section 2.3. Another royal jelly acid [2-decenedioic acid (149)] was prepared by cobalt carbonyl-catalyzed carbonylation of the terminal double bond, followed by isomerization of the double bond to the conjugated position to afford 149[122], Hexadecane-2,15-dione (150) can be prepared by Pd-catalyzed oxidation of the terminal double bond, hydrogenation of the internal double bond, and coupling by Kolbe electrolysis. Aldol condensation mediated by an organoaluminum reagent gave the unsaturated cyclic ketone 151 in 65% yield. Finally, the reduction of 151 afforded muscone (152)[123]. n-Octanol is produced commercially as described beforc[32]. 

Pyrroles react with the conjugate acids of aldehydes and ketones to give carbinols (e.g. 67) which cannot normally be isolated but which undergo proton-catalyzed loss of water to give reactive electrophiles (e.g. 68). Subsequent reaction may lead to polymeric products, but in the case of reaction of pyrrole and acetone a cyclic tetramer (69) is formed in high yield. 

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