Aldehyde enones from

Route (b) offers a short cut since the reaction between (5) and PhCHO under dehydrating conditions needs no control as (3) is the only possible enone from a ketone enolate attacking the more reactive aldehyde (p T 167). The Michael reaction is also better by this route as explained on p T 171, This is the published synthesis. 

Carbonyl compounds from a-amino nitriles. A synthesis of a-hydroxy enones from the a-amino nitrile derivatives of enals starts from alkylation with aldehydes and the hydrolysis of the products. ... 

Enones from two different aldehydes The silyldibromolithium reagent Pitches two aldehydes on itself, becoming the a-carbon of the resulting enone system. After union with the first aldehyde molecule the nucleophilic site is regenerated by treatment with yec-BuLi in a one-pot reaction. 

As already indicated, carbonyl compounds such as ketones, aldehydes, enones, and quinones possess the property to act as effective electron acceptors in the excited state for generating radical anions in the presence of electron-donating partners such as alkenes, aromatics, ruthenium complexes, amines, and alcohols. We will not consider the reactivity of enones and quinones, but we will focus our attention on the behavior of the radical anions formed from ketones and aldehydes. Four different processes can occur from these radical anions including coupling of two radical anions and/or coupling of the radical anion with the radical cation formed from the donor, abstraction of hydrogen from the reaction media to produce alcohols, cyclization, in the case of ce-unsaturated radical anions, and fragmentation when a C -X bond (X=0, C) is present (Scheme 18). 

The compounds 26 and 30 were also used for his methynolide synthesis. The aldehyde derived from 26 reacted with crotyltributylstannane to give stereoselectively 121, which was selectively protected to the alcohol 122. This alcohol was transformed into the ketophosphonate carboxylic acid 123. Yamaguchi esterification of 30 with 123 gave the corresponding ester, which was cyclized by Nicolaou method to give the 14-membered enone 124. Selective deprotection of the DMPM group with DDQ followed by Swem s oxidation... 

Preparation of enones from saturated ketones by Pd(II)-promoted dehydrosilyla-tion via silyl enol ethers was reported by Ito. Transmetallation of the silyl enol ether of cyclohexanone 519 with Pd(OAe)2 gives the oxo-TT-allylpalladium complex 520 (Pd enolate), which undergoes -H elimination to afford cyclohexenone. BQ is used as an oxidant of Pd(0) [211], However, the enone formation can be carried out using a catalytic amount of Pd(OAc)2 in DMSO under oxygen without other oxidants at room temperature. Also aldehyde 521 is converted to unsaturated aldehyde 522 via silyl ether in DMSO [4],... 

MSA can be used as a powerful, safe, and recyclable catalyst for the condensation reaction of cyclic 1,3-diketones with arylaldehydes (Scheme 3.25). Firstly, synthesis of 2,2-(arylmethylene)bis(3-hydroxycyclohex-2-enone) from reaction of cyclic 1,3-diketones with several aromatic aldehydes was expected, but, as can be seen from Scheme 3.25, under the given conditions, 2,2 -(arylmethylene)bis(3-hydroxycyclohex-2-enone) was not formed and cyclic 1,3-diketones with aldehydes were effectively cyclized to give 9-aryl-substituted 1,8-dioxooctahydroxanthenes. 

Now we look at enones from the opposite point of view—how do we disconnect them If we look at the bond that has been made in each of the previous examples (highlighted in red), it is clear that we must dissect the enone or enal through the double bond to give two carbonyl compounds or a dicarbonyl compound. Consider 20.11 (Figure 20.20). We disconnect the double bond so that there is a carbonyl group at one side of it and an enolizable site at the other. If we consider the forward reaction in this case, there should be no problem with it, because only the ketone is able to enolize, but the aldehyde is the more electrophilic component. Most bases will be appropriate here in practice, sodium hydroxide in aqueous ethanol was used. 

Ailyl enol carbonates derived from ketones and aldehydes undergo Pd-cat-alyzed decarboxylation-elimination, and are used for the preparation of a, /3-unsaturated ketones and aldehydes. The reaction is regiospecific. The regio-isomenc enol carbonates 724 and 726, prepared from 723, are converted into two isomeric enones, 725 and 727. selectively. The saturated aldehyde 728 can be converted into the a,/3-unsaturated aldehyde 730 via the enol carbonate 729[459]. 

In a more elaborate and specific synthesis, the terpenoid indole skeleton found in haplaindole G, which is isolated from a blue-green alga, was constructed by addition of a nucleophilic formyl equivalent to enone 6.5A. Cyelization and aromatization to the indole 6.6B followed Hg -catalysed unmasking of the aldehyde group[6]. 

Conjugate addition of methyl magnesium iodide in the presence of cuprous chloride to the enone (91) leads to the la-methyl product mesterolone (92) Although this is the thermodynamically unfavored axially disposed product, no possibility for isomerization exists in this case, since the ketone is once removed from this center. In an interesting synthesis of an oxa steroid, the enone (91) is first oxidized with lead tetraacetate the carbon at the 2 position is lost, affording the acid aldehyde. Reduction of this intermediate, also shown in the lactol form, with sodium borohydride affords the steroid lactone oxandrolone... 

The aldol reaction yields either a /3-hydroxy aldehyde/ketone or an a, 3-unsatu-rated aldehyde/ketone, depending on the experimental conditions. By learning how to think backward, it s possible to predict when the aldol reaction might be useful in synthesis. Whenever the target molecule contains either a /3-hydroxy aldehyde/ketone or a conjugated enone functional group, it might come from an aldol reaction. 

What ketones or aldehydes might the following enones have been prepared from by aldol reaction ... 

The aldehyde function at C-85 in 25 is unmasked by oxidative hydrolysis of the thioacetal group (I2, NaHCOs) (98 % yield), and the resulting aldehyde 26 is coupled to Z-iodoolefin 10 by a NiCh/CrCH-mediated process to afford a ca. 3 2 mixture of diaste-reoisomeric allylic alcohols 27, epimeric at C-85 (90 % yield). The low stereoselectivity of this coupling reaction is, of course, inconsequential, since the next operation involves oxidation [pyridinium dichromate (PDC)] to the corresponding enone and. olefination with methylene triphenylphosphorane to furnish the desired diene system (70-75% overall yield from dithioacetal 9). Deprotection of the C-77 primary hydroxyl group by mild acid hydrolysis (PPTS, MeOH-ClHhCh), followed by Swem oxidation, then leads to the C77-C115 aldehyde 28 in excellent overall yield. 

Advanced Example In research on violet perfumes, aldehyde (33) became a key Intermediate for a new series of compounds. Dlels-Alder disconnection gives acrolein and diene (34) which can he made by the Grignard method from available enone (36),... 

Non-conjugated enone (31) is clearly a Birch reduction product from ether (33). Grlgnard disconnection leaves aldehyde (34), and FGA reveals a condensation product from (35). 

The reaction of the aldehyde 174, prepared from D-glucose diethyl dithio-acetal by way of compounds 172 and 173, with lithium dimethyl methyl-phosphonate gave the adduct 175. Conversion of 175 into compound 176, followed by oxidation with dimethyl sulfoxide-oxalyl chloride, provided diketone 177. Cyclization of 177 with ethyldiisopropylamine gave the enone 178, which furnished compounds 179 and 180 on sodium borohydride reduction. 0-Desilylation, catalytic hydrogenation, 0-debenzyIation, and acetylation converted 179 into the pentaacetate 93 and 5a-carba-a-L-ido-pyranose pentaacetate (181). 

An unusual reaction was been observed in the reaction of old yellow enzyme with a,(3-unsat-urated ketones. A dismutation took place under aerobic or anaerobic conditions, with the formation from cyclohex-l-keto-2-ene of the corresponding phenol and cyclohexanone, and an analogous reaction from representative cyclodec-3-keto-4-enes—putatively by hydride-ion transfer (Vaz et al. 1995). Reduction of the double bond in a,p-unsaturated ketones has been observed, and the enone reductases from Saccharomyces cerevisiae have been purified and characterized. They are able to carry out reduction of the C=C bonds in aliphatic aldehydes and ketones, and ring double bonds in cyclohexenones (Wanner and Tressel 1998). Reductions of steroid l,4-diene-3-ones can be mediated by the related old yellow enzyme and pentaerythritol tetranitrate reductase, for example, androsta-A -3,17-dione to androsta-A -3,17-dione (Vaz etal. 1995) and prednisone to pregna-A -17a, 20-diol-3,ll,20-trione (Barna et al. 2001) respectively. 

Enynes 71 react with aldehydes 61 in the presence of the [Ni(COD)J/SIPr catalytic system to afford two distinct products 72 and 73 (Scheme 5.20) [20b], The enone 72 is derived from aldehyde addition with the alkyne moiety while the adduct 73 arises from the aldehyde addition with the alkene moiety. The product distribution is dependent on the substituent on either the alkyne or alkene moieties. The reaction between 71 and ketones 74 led to the unprecedented formation of pyrans 75 (Scheme 5.20). The reaction showed to be highly regioselective in aU the cases, the carbonyl carbon was bound to the olefin. 

The intermediate enolate or enol ether from the initial reduction of an enone may be alkylated in situ (Eq. 281).455 / -Substituted cyclopentenones may be asymmetrically reduced and alkylated459 (see section on asymmetric reductions of enones). Enolates may also be trapped with an aldehyde in a reductive aldol condensation of an enone with an aldehyde,455 permitting a regioselective aldol condensation to be carried out as shown in Eq. 282.455 This class of reductive aldol condensation reactions can also occur in a cyclic manner (Eq. 283).460... 

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