Diketones unsaturated, reduction

The synthesis of unsymmetrical 1,4-diketones results from the conjugate addition of the nitronate anion (as the acyl anion equivalent) to an a,fi-unsaturated ketone [Method (6)].l47a The intermediate nitroketone is converted into the diketone by reduction with titanium(m) chloride at pH 1, or by ozono-lysis of the nitronate anion147b (cf. Section 5.7.7, p. 599). 

The reduction of ,/S-unsaturated y-diketones can conveniently be done with zinc in acetic acid. The following procedure is applicable to the reduction of the Diels-Alder adduct of quinone and butadiene (Chapter 8, Section II). 

An interesting use of the diketone type of ketene dimer (34) is reduction and cleavage to B,y-unsaturated aldehyde (35),... 

The reductive animation of 1,4-diketones in the presence of an equivalent of ammonia opens an avenue to 2,4-disubstituted pyrrolidines. Since Stetter s thiazolium salt chemistry allows the preparation of 1,4-diketones from a, 3 unsaturated enones and aldehydes, a large variety of pyrrolidines may be prepared. Two examples of such syntheses have recently been published by the T. H. Jones group (Scheme 27) (132, 170). 

One-electron reduction of unsaturated a,8-diketones may sometimes generate a diene structure and initiate condensation. Thus, triazoledions (TAD) pass into tetraazabicyclooctanetetraones (TABO). Naphthalene-sodium (ca. 1 mol%), sodium metal, or even sodium iodide efficiently catalyzes the reaction. Tetracyanoethyene and lead tetraacetate retard it. Consequently, the condensation has a chain character (Borhani and Greene 1986 Scheme 7.30). 

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. 

One-electron reduction of a,/l-unsaturated ketones yields, instead of pina-cols, e-diketones formed by coupling of semireduced species at the /3-carbons... 

For a review of Clemmensen reduction of diketones and unsaturated ketones, see Buchanan Woodgate Q. Rev. Chem. Soc. 1969, 23, 522-536. 

The lower members of the homologous series of 1. Alcohols 2. Aldehydes 3. Ketones 4. Acids 5. Esters 6. Phenols 7. Anhydrides 8. Amines 9. Nitriles 10. Polyhydroxy phenols 1. Polybasic acids and hydro-oxy acids. 2. Glycols, poly-hydric alcohols, polyhydroxy aldehydes and ketones (sugars) 3. Some amides, ammo acids, di-and polyamino compounds, amino alcohols 4. Sulphonic acids 5. Sulphinic acids 6. Salts 1. Acids 2. Phenols 3. Imides 4. Some primary and secondary nitro compounds oximes 5. Mercaptans and thiophenols 6. Sulphonic acids, sulphinic acids, sulphuric acids, and sul-phonamides 7. Some diketones and (3-keto esters 1. Primary amines 2. Secondary aliphatic and aryl-alkyl amines 3. Aliphatic and some aryl-alkyl tertiary amines 4. Hydrazines 1. Unsaturated hydrocarbons 2. Some poly-alkylated aromatic hydrocarbons 3. Alcohols 4. Aldehydes 5. Ketones 6. Esters 7. Anhydrides 8. Ethers and acetals 9. Lactones 10. Acyl halides 1. Saturated aliphatic hydrocarbons Cyclic paraffin hydrocarbons 3. Aromatic hydrocarbons 4. Halogen derivatives of 1, 2 and 3 5. Diaryl ethers 1. Nitro compounds (tertiary) 2. Amides and derivatives of aldehydes and ketones 3. Nitriles 4. Negatively substituted amines 5. Nitroso, azo, hy-drazo, and other intermediate reduction products of nitro com-pounds 6. Sulphones, sul-phonamides of secondary amines, sulphides, sulphates and other Sulphur compounds... 

Thiophenecarbaldehydes add smoothly to a,f3-unsaturated ketones and nitriles under cyanide ion catalysis to form y-diketones (366) and y-ketonitriles (367) respectively (76CB534). The 2,5-dicarbaldehyde gives the bis-adduct (368). The aldehydes undergo normal reduction to the hydroxymethylthiophenes by sodium borohydride. However, electrochemical reduction of the 2,5-dialdehyde on a mercury electrode at pH 1-3 gives the bimolecular reduction product (369) as a mixture of meso- and ( )-forms in the ratio 7 3. Reduction with zinc and acetic acid gives only the meso -form of (369) (75CR(C)(280)165>. 

After 16 hours on stream, no more unsaturated diketone 2 was formed and the addition of I to the reactant gas feed was stopped. The oven was maintained at 200°C and 02 was added to the gas feed. The temperature in the catalyst bed increased instantaneously by ca. 30°C. The temperature decreased gradually during the following 1.5 hours reaching a final value of 200°C. This behaviour is attributed to the reduction of the catalyst during the 16h period in which it was on stream and exothermic reoxidation of Cu-metal to copper oxide. This indicates that oxygen of the catalyst is consumed in the conversion process of L... 

With sodium borohydride and catalytic amounts of titanyl acetoacetonate, a,fi-unsaturated carbonyl compounds give allyl alcohols regioselectively, whereas a-diketones and acyloins are reduced to vicinal diols.325 Enantioselectivities in the reduction of acetophenone, catalysed by 1,3,2-oxazaborolidones, have been examined using the AM1-SCF MO method. The optimized geometries, thermal enthalpies, and entropies of R and S transition states in the stereo-controlling steps of the reduction have been obtained.326... 

The following tables are intended to include all the reductions with aluminum alkoxides which were reported prior to February, 1943, although some examples doubtless have been overlooked. Table I lists the reduction of aldehydes, which have been subdivided into (a) aliphatic aldehydes and (b) alicyclic and aromatic aldehydes. Table II lists the reduction of ketones, which have been classified as (a)-satu-rated and unsaturated aliphatic ketones, (b) aromatic ketones, (c) alicyclic ketones, (d) unsaturated alicyclic and aromatic ketones, (e) a- — halogen substituted ketones, (f) diketones, (g) protected diketones, (h) alcoholic and phenolic ketones (and ethers or esters of these), and (i) keto esters. 

The reaction involves a Pummerer-type rearrangement to a a-thiocarbocation, which then reacts with the enol silyl ether. The products can be converted by reduction into 1,4-diketones or by oxidation to unsaturated 1,4-diketones. 

Three main types of redox reactions of keto compounds leading to the formation of metal enolates have been reported (i) two-electron reduction of diketones or a,(f-unsaturated ketones or esters (equation 1), (ii) oxidative addition reactions (equation 2) and (iii) threefold deprotonation of diketoamines followed by a two-electron oxidation of the trianion by the metal (equation 3). 

Quinones are cyclic unsaturated diketones in which the carbon atoms are derived from the oxidation of an aromatic system. Although the underlying reactivity of quinones is that of unsaturated ketones (cyclohexadi-enediones), it is tempered by this relationship to aromatic compounds and in particular by their reduction to dihydroxyphenols (quinols). 

Reductions of symmetrical bicyclic diketones may also be effected selectively, as illustrated in Scheme 12. The stereospecificities of the HLADH-catalyzed transformations of the unsaturated decalin-diones (25) and (27) to the corresponding hydroxy ketones (26) and (28), and in fact all specificity aspects of this enzyme, are fully predictable using a simple to use, cubic-space model of the enzyme s... 

A number of side reactions have been reported to occur during Wolff-Kishner reductions in addition to those discussed above. In particular, cleavage of strained rings located adjacent to the carbonyl may accompany reduction to afford saturated and/or alkene products. For example, the pentacyclic diketone (41) afforded the unsaturated tetracyclic compound (42) and saturated derivative (43) in addition to the normal Wolff-Kishner product (44 equation 13). Likewise, the cyclopropyl ring in alkaloid (45) suffered cleavage during reduction to give the alkene (46 65% equation 14). ... 

Reductive dimerization of a,p-unsaturated ketones is effected by either Cr" or V" chloride to give 1,6-diketones, but aliphatic a, -unsaturated aldehydes are dimerized to the allylic glycals. Interestingly, nonconjugated aldehydes are stable towards these reagents. Similar pinacolic couplings of aldehydes and ketones with Ti" reagents were developed by Corey. ... 

Reduction of enol ethers or enol esters of 1,3-diketones, followed by acid-catalyzed allylic rearrangement of the reduction product (see p. 85 in ref. 5) is a useful route to a,P-unsaturated ketones. Ali-phatic - and alicyclic enones have thus been prepared in good yields at low temperatures with NaAlH2(0CH2CH20Me)2.2 6... 

Lactone. Various fungi, including Bakers yeast and Geotrichum candi-dum, have been shown to produce optically active lactones, useful chiral synthon, via the stereoselective reduction of suitable unsaturated precursors (42). Figure 15 shows the production scheme for a chiral, substituted diketone, a synthon for optically active carotenoids. 

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