Diketones, reaction with compounds

The Michael reaction is of central importance here. This reaction is a vinylogous aldol addition, and most facts, which have been discussed in section 1.10, also apply here the reaction is catalyzed by acids and by bases, and it may be made regioselective by the choice of appropriate enol derivatives. Stereoselectivity is also observed in reactions with cyclic educts. An important difference to the aldol addition is, that the Michael addition is usually less prone to sterical hindrance. This is evidenced by the two examples given below, in which cyclic 1,3-diketones add to o, -unsaturated carbonyl compounds (K. Hiroi, 1975 H, Smith, 1964). 

Terminally unsaturated fluonnated alkenoic acids can be obtained from poly-fluorocycloalkenes by reaction with potassium hydroxide m rert-butyl alcohol [24] (equation 26) The use of a tertiary alcohol is critical because primary and secondar y alcohols lead to ethers of the cycloalkenes The use of a polar aprotic solvent such as diglyme generates enols of diketones [26] (equation 27) The compound where... 

The reaction of (fluoroalkenyl)carboranes with potassium permanganate in acetone leads to formation of a-diketones [119. These compounds react by photochemical reaction in which the radical formation at boron is followed by addition to the double bond [120] (equation 92). 

Reaction type 3 (equation 10), where the complete hetero-l,3-diene skeleton is incorporated into the newly formed ring system, occurs with compounds having both a nucleophilic center and an electrophilic center If these two functionalities are in positions 1 and 2, various types of six-membered ring systems become accessible 4,4-Bis(trifluoromethyl)-I,3-diaza-1,3-butadienes require only room temperature to react with acetyl cyanide to yield l,4,5,6-tetrahydropynmidin-6-ones [96] Likewise, certain open-chain 1,3-diketones (acetylacetone and acetoacetates) and the heterodiene form six-membered nng systems [97] (equation 19)... 

Julid investigated the behavior of terfuran 22 and bis(thienyl)furan 23 by cyclic voltammetry as well as the EPR spectra of the radical cations derived from these two compounds. Condensation of the diketone 20 with sulfuric acid furnished furan 22 in 18% yield, while reaction of diketone 21 with hydrochloric acid produced 23 in 84% yield.In a related report, Luo prepared oligomeric bis(thienyl)furans via similar methodology. ... 

In a modified approach, the carbolinyl acetate 393 underwent a Mannich reaction with formaldehyde and acetone to give the keto ester 396 which, with base, cyclized to the diketone 397. This diketone (397) has recently been used to prepare a number of interesting pentacyclic compounds. 

The net effect of the Stork reaction is the Michael addition of a ketone to an cn/3-unsaturated carbonyl compound. For example, cyclohexanone reacts with the. cyclic amine pyrrolidine to yield an enamine further reaction with an enone such as 3-buten-2-one yields a Michael adduct and aqueous hydrolysis completes the sequence to provide a 1,5-diketone (Figure 23.8). 

Barbituric acid can be considered as a cyclized malonic acid diamide (malonyl-urea). It is therefore a cyclic diketone that may be classified, in the sense of the compounds discussed in Section 12.6, as a coupling component with a methylene group activated by two carbonyl groups in the a- and a -positions. The reaction with arenediazonium salts was studied by Nesynov and Besprozvannaya (1971). These authors obtained coupling products (in good yield) that they considered to be arylhydrazones. Coupling with 4-(phenylazo)benzenediazonium chloride was studied by Chandra and Thosh (1991). The lH NMR spectra of these compounds are consistent with the arylhydrazone structure 12.68. 

The base-stabilized germanimine (Me2Si)2(N-t-Bu)4Ge=N(SiMe3) does not react with benzophenone, even upon heating.72 Apparently, no other reactions between stable germanimines and simple carbonyl compounds have been investigated however, the reaction with a diketone, 3,5-di-r-butyl-ort/io-quinone, has. Both a [2 + 2] and a [2 + 4] cycloaddition reaction have been postulated the initially formed adducts are unstable and decompose (see Scheme 4). 

The five-coordinate complexes Ir(CO)(PPh3)2L, where HL = /3-diketone, A-benzoyl-A-phenyl-hydroxylamine, salicylaldehyde, 8-hydroxyquinoline, 2-hydroxybenzophenone, 2-hydroxy-8-methoxybenzophenone, were prepared from [Ir(CO)(PPh3)2Cl].632 The resulting compounds all underwent oxidative addition reactions with Br2. Reaction of [(cod)2IrCl]2 with N-substituted 3-hydroxy-2-methyl-4-pyridine gives the bichelated complex (389). 33... 

Both overt carbanions and organometallic compounds, such as Grignard reagents, are powerful nucleophiles as we have seen in their addition reactions with C=0 (p. 221 et seq.) they tend therefore to promote an SN2 pathway in their displacement reactions. Particularly useful carbanions, in preparative terms, are those derived from CH2(C02Et)2, (3-ketoesters, l,3-( 3-)diketones, e.g. (55), a-cyanoesters, nitroalkanes, etc.—the so-called reactive methylenes ... 

The Nef reaction can also be carried out with reducing agents. Aqueous titanium chloride reduces nitro compounds to imines, which are readily hydrolyzed to carbonyl compounds (Eq. 6.17).28 The Michael addition of nitroalkanes to enones followed by reaction with TiCl3 provides an excellent route to 1,4-diketones and hence to cyclopentenones. For example, cw-jasmone is readily obtained,28 as shown in Eq. 6.18. 

Aside from alcohols, other oxygen nucleophiles have also participated in hydroalkoxylation reactions with alkynes. The most common of these are 1,3-dicarbonyl compounds, whose enol oxygens are readily available to add to alkynes. Cyclization reactions of this type have been carried out under Pd(0) catalysis with various aryl or vinyl iodides or triflates, often in the presence of CO, affording the corresponding furan derivatives (Equation (95)).337-340 A similar approach employing cyclic 1,3-diketones has also been reported to prepare THFs and dihydropyrans under Pd, Pt, or W catalysis.341 Simple l-alkyn-5-ones have also been isomerized to furans under the influence of Hg(OTf)2.342... 

E)- or (Z)-y-alkoxyallylstannanes, Bu3SnCH2CH=CHOR, undergo a light-promoted reaction with various classes of carbonyl compounds (aldehydes, ketones, O -diketones) to give homoallylic alcohols with retention of double-bond geometry. 

Diketone 829 closely parallels 820 in its chemical reactivity. Introduction of a functionalized bridging carbon can be achieved with ethyl formate and base . The acetate group in 8JO 6 is remarkably easily replaced with retention by simple nucleophiles, e.g, the conversion to 8JI. The implicated peristyl-3-ene-2,6-dione (8J2) can in fact be obtained as a colorless crystalline compound. Also, 8J0a spontaneously dehydrates during ketalization to produce 8JJ. The strained double bond in 832 enters readily into Diels-Alder reaction with furan to furnish a 3 1 mixture of 834a and 834b. 

It has been observed in CVD as well as in ALD depositions that coordi-natively unsaturated y0-diketonate-type compounds may oligomerise or react with the environment and become less volatile [15,16,66,67]. This is a cause of instability, especially with larger and basic central ions such as strontium and barium. y0-diketonate-type chelates can be protected against oligomerisation and roomOtemperature reactions with moisture by adducting them with neutral molecules (Fig. 4) [68-71]. 

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