Heteroaromatic Ketones

In the reaction of Q,/3-unsaturated ketones and esters, sometimes simple Michael-type addition (insertion and hydrogenolysis, or hydroarylation, and hydroalkenylation) of alkenes is observed[53,54]. For example, a simple addition product 56 to methyl vinyl ketone was obtained by the reaction of the heteroaromatic iodide 55[S5]. The corresponding bromide affords the usual insertion-elimination product. Saturated ketones are obtained cleanly by hydroarylation of o,/3l-unsaturated ketones with aryl halides in the presence of sodium formate, which hydrogenolyses the R—Pd—I intermediate to R— Pd—H[56]. Intramolecular hydroarylation is a useful reaction. The diiodide 57 reacts smoothly with sodium formate to give a model compound for the afla-toxin 58. (see Section 1.1.6)[57]. Use of triethylammonium formate and BU4NCI gives better results. 

Photopolymerization reactions are widely used for printing and photoresist appHcations (55). Spectral sensitization of cationic polymerization has utilized electron transfer from heteroaromatics, ketones, or dyes to initiators like iodonium or sulfonium salts (60). However, sensitized free-radical polymerization has been the main technology of choice (55). Spectral sensitizers over the wavelength region 300—700 nm are effective. AcryUc monomer polymerization, for example, is sensitized by xanthene, thiazine, acridine, cyanine, and merocyanine dyes. The required free-radical formation via these dyes may be achieved by hydrogen atom-transfer, electron-transfer, or exciplex formation with other initiator components of the photopolymer system. 

Silylated cyanohydrins have also been prepared via silylation of cyanohydrins themselves and by the addition of hydrogen cyanide to silyl enol ethers. Silylated cyanohydrins have proved to be quite useful in a variety of synthetic transformations, including the regiospecific protection of p-quinones, as intermediates in an efficient synthesis of a-aminomethyl alcohols, and for the preparation of ketone cyanohydrins themselves.The silylated cyanohydrins of heteroaromatic aldehydes have found extensive use as... 

A special application of heteroaromatic acylation via a modified Dakin-West reaction leads to a-fluoro ketone derivatives [50] (equation 30) Such fluoro ketones have been successfully used as enzyme inhibitors in modern bioorganic chemistry [5, 6]... 

In a more general approach toward pentacyclic heteroaromatics from tricyclic ketones, treatment of the N-methylated derivative of 112 with p-tolylhydrazine, followed by Fischer indolization of the resulting phenylhydrazone in a mixture of trifluoroacetic acid and acetic acid, produced only a low yield of 114, although this method proved to be considerably mrae efficient for synthesis of analogous systems containing other heteroatoms than nitrogen (98SC1239). 

A range of electron-withdrawing groups on the nitrogen - N-P(0)Ph2, N-tosyl, and N-SES, for example - were tolerated. Imines derived from aromatic, heteroaromatic, unsaturated, and even aliphatic aldehydes and ketones were employed... 

Besides aromatic hydrocarbons such as pyrene (above), benzanthracene (Becker et al., 1977a), benzoin derivatives (Baumann et al., 1982), aromatic and heteroaromatic ketones (Fomin et al., 1980 Baumann et al., 1985), azo dyes (Timpe et al., 1982), methylene blue (Becker et al., 1986 a Becker and Kohrs, 1990), acridine yellow... 

In the Diels-Alder reaction with inverse electron demand, the overlap of the LUMO of the 1-oxa-l,3-butadiene with the HOMO of the dienophile is dominant. Since the electron-withdrawing group at the oxabutadiene at the 3-position lowers its LUMO dramatically, the cycloaddition as well as the condensation usually take place at room or slightly elevated temperature. There is actually no restriction for the aldehydes. Thus, aromatic, heteroaromatic, saturated aliphatic and unsaturated aliphatic aldehydes may be used. For example, a-oxocarbocylic esters or 1,2-dike-tones for instance have been employed as ketones. Furthermore, 1,3-dicarbonyl compounds cyclic and acyclic substances such as Meldmm s acid, barbituric acid and derivates, coumarins, any type of cycloalkane-1,3-dione, (1-ketoesters, and 1,3-diones as well as their phosphorus, nitrogen and sulfur analogues, can also be ap-... 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

The a-oxoketene dithioacetals 6 (6.1-6.43) employed in this work as three carbon 1,3-biselectrophilic components have been drawn from various active methylene ketones and are described in the Table-1. The corresponding a-oxoketene N,S- and 0,S-acetals (17.1- 17.15) which are usually derived from a-oxoketene dithioacetals are described in Table-2. These examples are only a representative groups to demonstrate the general application of the new Jl-heteroaromatic annulation methodology... 

The above examples represent Jl-heteroaromatic annulation involving the reaction of allyl anions whose double bond is a part of the heterocyclic ring system (Scheme 1). The corresponding a-oxoketene dithioacetals (1,3-electrophilic component) were generally derived from nonheterocyclic carbonyl precursors. Alternatively the Jl-heteroaromatic annulation can also be employed to a-oxoketene dithioacetals derived from heterocyclic ketones (1,3-bielectrophile) and hetero/nonheteroallyl anions (1,3-binucleophile). These reactions are described below. 

General enantioselective hydrogenation of heteroaromatic ketones is achieved by means of the XylBINAP/DAlPEN-Ru complexes and (CH3)3COK in 2-propanol. A variety of substrates with an electron-rich and -deficient heteroaromatic func-... 

Thus, the unsubstituted starting compound 69 was treated with resorcinol in the presence of trifluoroacetic acid (TFA) to yield 70. Then, reaction of 69 with the cyclic a,/3-unsaturated ketone in the presence of lithium hydride gave the 7-substituted heteroaromatic compound 71, and ethyl cyanoacetate afforded the cross-conjugated product 72, whereas reaction with pyrimidine-2,4,6-trione in the presence of triethylamine yielded the addition product 73. Indole also been reacted with 69, and heating of the dichloromethane solution for 90 min in the presence of TFA yielded the addition product 74 in excellent yield (95%) <1998ZOR450> (Scheme 12). 

For more volatile compounds in soils, such as aromatic hydrocarbons, alcohols, aldehydes, ketones, chloroaliphatic hydrocarbons, haloaromatic hydrocarbons, acetonitrile, acrylonitrile and mixtures of organic compounds a combination of gas chromatography with purge and trap analysis is extremely useful. Pyrolysis gas chromatography has also found several applications, heteroaromatic hydrocarbons, polyaromatic hydrocarbons, polymers and haloaromatic compounds and this technique has been coupled with mass spectrometry, (aliphatic and aromatic hydrocarbons and mixtures of organic compounds). 

The reactivity of heterocyclic systems with carbenes, generated under phase-transfer catalytic conditions, has been reviewed for the period up to 1983 [1]. Most unsaturated non-heteroaromatic systems react with carbenes in the manner expected of alkenes, amines, amides, ketones, etc. (see Sections 7.3,7.5 and 7.6). 

In addition, unstabilized enolate nucleophiles have been generated by decarboxylation of (3-ketocarboxylates. In this case, no additives are required to activate the nucleophile, but the highest yields and selectivities were obtained in the presence of two equivalents of DBU [82]. Although reactions of allylic carbonates containing aromatic, heteroaromatic, and aliphatic substituents occurred, only reactions to form aryl ketone products were published. 

Sulfonated poly(arylene ether)s have shown promise for durability in fuel cell systems, while poly-(styrene)- and poly(imide)-based systems serve as model systems for studying structure-relationship properties in PEMs because their questionable oxidative or hydrolytic stability limits their potential application in real fuel cell systems. Sulfonated high performance polymer backbones, such as poly(phe-nylquinoxaline), poly(phthalazinone ether ketone)s, polybenzimidazole, and other aromatic or heteroaromatic systems, have many of the advantages of poly-(imides) and poly(arylene ether sulfone)s and may offer another route to advanced PEMs. These high performance backbones would increase the hydrated Tg of PEMs while not being as hydrolytically sensitive as poly(imides). The synthetic schemes for these more exotic macromolecules are not as well-known, but the interest in novel PEMs will surely spur developments in this area. 

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