Conjugation influence ketones

Of mechanistic interest is the question of whether these cyclic ketones come directly from conjugated diene intermediates or from PdCl2 complexes of carboxyoctadecenoates. Yields of cyclic ketones 4 are actually of the same order of magnitude from linoleate as from its conjugated diene isomers (Runs 7 and 8, Table I). Studies were also made to determine if yields of cyclic ketones can be influenced by the amount of H20 used. However, in experiments using no added H20 and one-tenth the stoichiometric amount of H20, only 10 and 8% ketones and conversions (diene disappearance) of only 58 and 78% were obtained, respectively. 

Stereoelectronic effects should also play an important role in the nucleophilic 1,4-additions of anions to conjugated systems. These effects should therefore influence the Michael reaction as well as the hydrocyanation of a,6-unsaturated ketones. Studies on these reactions provided evidence that the kinetically controlled addition of a nucleophile to a cyclohexenone derivative is indeed subject to stereoelectronic effects. 

Conjugation has a great influence on the structure of aliphatic and alicyclic compounds. Thus, the existence of an amino form has been established (in addition to the extreme case of aromatic amines17) for all compounds where the double bond is conjugated with a carbonyl group (or its equivalent),12 with esters12,18 and nitriles of a,/8-un-saturated /8-amino acids,519,20 and with /8-amino-ketones. The /3-keto-esters ethyl 2-cyclopentanone- 1-carboxylate and ethyl 2-cyclo-hexanone-l-carboxylate exist as mixtures containing 95% of the keto... 

Notice that in these compounds the ketone is not conjugated to any of the alkenes and so does not influence the reaction. If we increase the reactivity of the dienophile by putting an ester group in conjugation with it, most of the compound does the Diels-Alder reaction before it does the [1,5]H shift. 

The formation of carbon-carbon bonds by conjugate addition of carbonucleophiles to a,/3-unsaturated systems has been studied intensively and reviewed over the past few years . Interestingly, applications with simple, unstabilized lithium enolates are relatively rare. Most reported examples are limited to the addition of stabilized enolates, such as those derived from malonates or acetoacetates. Nevertheless, some diastereo- and enantioselective versions of the conjugate addition, even with unstabilized lithium enolates, are well known. In 2004, Tomioka and coworkers studied the influence of a chiral diether (191) on the 1,4-addition of lithium ester enolates (189) to a,-unsaturated ketones (equation 51) . Their investigations showed that good enantioselectivities were obtained with cyclic enones, like 2-cyclopentenone (190) addition to a mixture of 189 and 191 gave the desired 1,4-adduct (R)-192 with 74% ee, but only 47% yield. Unfortunately, also the Peterson product 193 was formed in a yield of 22% by initial 1,2-addition of the enolate to the Michael acceptor. 

The reduction of a,p-unsaturated aldehydes and ketones by NaBH4 leads, in general, to substantial amounts of fully saturated alcohols. In alcoholic solvents, saturated -alkoxy alcohols can be formed via conjugate addition of the solvent. This latter process becomes the main reaction path when reduction is performed in 2-propanol in the presence of sodium isopropoxide. In base, a homoallylic alcohol can become the major product of borohydride reduction of an enone. Analysis of the influence of substrate structure on NaBH4 reduction has shown that increasing steric hindrance on the enone increases 1,2-attack. ... 

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. 

Aryl transfer. The aryl group of ArSnMcj is selectively transferred to aldehydes and to the P-position of conjugated ketones and esters, under the influence of the ionic Rh complex. 

Salomon and his coworkers have over the years studied the influence of copper(I) triflate on the cyclization of non-conjugated dienes. In the present example the diene (170) is converted readily on irradiation in the presence of the catalyst and affords the alcohol (171). This is oxidised to the corresponding ketone. The intramolecular cyclization of the diene (172), using a copper triflate catalyst, affords the straight (2-1-2) adduct (173). This cyclization was used as an approach to the synthesis of RobustadiaJ B. However, it was shown that the proposed structure of the natural product was wrong and that the robustadials should have the camphahe moiety in their structure as shown in (174). ... 

Rann et al. reported the dramatic influence of a new tailor-made, task-specific, and stable ionic liquid, butyl methyl imidazolium hydroxide ([bmim][OH]), in Michael addition. They have discovered that a task-specific ionic liqnid [bmim][OH] efficiently promoted the Michael addition of 1,3-dicarbonyl compounds, cyano esters, and nitro alkanes to a variety of conjugated ketones, carboxylic esters, and nitriles withont reqniring any other catalyst and solvent (Fig. 12.21) [16]. Very interestingly, all open-chain 1,3-dicarbonyl componnds such as acetylacetone, ethyl ace-toacetate, diethyl malonate, and ethyl cyanoacetate reacted with methyl vinyl ketone and chalcone to give the usual monoaddition products, whereas the same reactions with methyl acrylate or acrylonitrile provided exclusively bis-addition products. 

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