Y-Arylated ketones

On the other hand, the arylative ring opening takes place in the presence of a Pd(0) catalyst, an aryl halide, and a base (Scheme 3, reaction b) [32-35]. Oxidative addition of aryl halides toward Pd(0) gives ArPdX species, which can readily interact with the alcohols affording arylpalladium alkoxide intermediates. Then, p-carbon elimination and subsequent reductive elimination occur to give y-arylated ketones and regenarate Pd(0) species. An example is shown in Eq. 15. 

Nishimura T, Uanura S (1999) Palladium-catalyzed arylation of tert-cyclobutanols with aryl bromide via C-C bond cleavage new approach fin the y-arylated ketones. J Am Chem Soc 121 (47) 11010-11011. doi 10.1021/ja993023q... 

Palladium(0)-catalyzed asymmetric arylation of tert-cyclobutanol 33 with bromobenzene, involving enantioselective C-C bond cleavage, furnished the chiral y-arylated ketone 34 (Scheme 3.13) [24]. Good enantioselectivity was observed when a chiral ferrocenyl P,N-ligand was used. y-Alkenylated and y-allenylated ketones were also obtained by asymmetric ring opening. 

When allylic alcohols are used as an alkene component in the reaction with aryl halides, elimination of /3-hydrogen takes place from the oxygen-bearing carbon, and aldehydes or ketones are obtained, rather than y-arylated allylic alcohoIs[87,88]. The reaction of allyl alcohol with bromobenzene affords dihydrocinnamaldehyde. The reaction of methallyl alcohol (96) with aryl halides is a good synthetic method for dihydro-2-methylcinnamaldehyde (97). 

The wide variety of ketomethylene and amino ketone monomers that could be synthesized, and the abiUty of the quinoline-forming reaction to generate high molar mass polymers under relatively mild conditions, allow the synthesis of a series of polyquinolines with a wide stmctural variety. Thus polyquinolines with a range of chain stiffness from a semirigid chain to rod-like macromolecules have been synthesized. Polyquinolines are most often prepared by solution polymerization of bis(i9-amino aryl ketone) and bis (ketomethylene) monomers, where R = H or C H, in y -cresol with di-y -cresyl phosphate at 135—140°C for a period of 24—48 h (92). 

Aryl ketones are also reduced with triethylsilane and TiCl4. This method can be used to prepare y-arylaminoacids.177... 

With compounds containing C—H bonds y to the carbonyl moiety, one often observes intramolecular hydrogen abstraction, in contrast to the in-termolecular hydrogen abstraction by aryl ketones discussed earlier in this... 

Treatment of a-(benzotriazol-l-yl)alkyl thioethers 831 with ZnBr2 weakens the bond with benzotriazole, and the obtained complex 832 may partially dissociate to thionium cation 835 that can be trapped by even mild nucleophiles. Thus, trimethylsilyl cyanide added to the reaction mixture causes substitution of the benzotriazole moiety by the CN group to give a-(phenylthio)carbonitrile 834. In a similar manner, treatment with allylsilane leads to y,S-unsaturated thioether 833. Addition of species 835 to the double bond of a trimethylsilyl ot-arylvinyl ether followed by hydrolysis of the silyloxy group furnishes (i-(phenylthio)alkyl aryl ketones 836 (Scheme 132) <1996TL6631>. 

These photoisomerizations can be solvent sensitive. For example, photolysis of the azepinone (42 R1 = aryl, R2 = Bu, R3 = H) in cyclohexane affords the azabicycloheptadiene (43 R1 = Ar, R2 = Bu , R3 = H) in 80% yield. Irradiation in methanol solution, however, affords a mixture of the two isomeric enols of the cyclopentenone (44 60%), and only 5% of the bicycle (43) (81JOC4077). Apparently, in aprotic solvents the azepine behaves photo-lytically as a heterocyclic conjugated triene, whereas in methanol its /3,-y- unsaturated ketone character predominates. 

Asymmetric Michael addition to to-nitrostyrenes,2 The enamine (2) formed from cyclohexanone and this prolinol derivative reacts with 2-aryl-1-nitroethylenes (3) to form, after acid hydrolysis of the primary adduct, essentially only one (4) of the four possible y-nitro ketones. 

Gallium(III) triflate catalysed the rearrangement of 2-substituted vinyl epoxides into /3,y-unsaturated carbonyl compounds with high regio- and chemo-selectivity with low catalyst loading. Alkyl-substituted trimethylsilylvinyl epoxides gave /i,y-unsaluralcd ketones, but aryl-substituted vinyl epoxides gave the aldehydes.80... 

However, the reduction potential of pthalimides is remarkably lower compared with aromatic ketones (e.g., V-methylphtalimide in DMF ed =— 1.37Y [25a], valerophenone ed =— 2.07 Y [30]). The radicals A and the radical anions B formed by hydrogen or electron transfer onto the triplet excited phthalimide are more stable than the corresponding species derived from aryl ketones (C and D), even though the triplet energies are very close (A is more stable than C by about 29 kJ/mol, Sch. 5) [31]. 

Substituents in a-Position. To rationalize the ratio between Norrish type II cleavage and cyclization (see preceding chapter) the influence of a-substituents on cyclization were studied exclusively on straight-chain aryl ketones with preferential y-hydrogen abstraction. 

Pioneering work on the photochemical diastereocontrol in zeolite supercages was reported by Turro and coworkers in 1991 [48]. They investigated the diastereoselective photodecarbonylation of 2,4-diphenyl-3-pentanone (DPP) adsorbed in various cation-exchanged X and Y zeolites to find that the diastereo-selectivity of d9l- over mestf-2,3-diphenylbutane increases in the order LiX NaX < LiY NaY < KY. In 1996, Ramamurthy and coworkers reported the first example of photochemical asymmetric induction in chirally modified zeolites [49], where they employed the Norrish/Yang type II reaction of cis-4-tert-butyl-cyclohexyl aryl ketones to the corresponding cyclobutanols. Since then, a variety of asymmetric photoreactions in zeolite supercages have been reported as reviewed below. 

To sum up, nucleophilic substitution at an olefinic carbon (at any rate, at the sharply electrophilic one, as in 3-substituted vinyl aryl ketones) involves addition of a nucleophile followed by formation of the PhC(0)CHCHXY anion, whose fate depends on the rate at w hich the group X leaves the molecule. If X leaves the molecule as soon as Y" attacks,... 

Asymmetric reduction of or y-functionalized alkyl aryl ketones provides a wide variety of chiral amino alcohols. Commercial -chloropropiophenone is reduced with borane-tetrahydrofuran adduct catalyzed by oxazaborolidine 45 to provide the chlorohydrin in over 99 % yield with 94 % ee. The resulting alcohol is a key intermediate for synthesis of the R form of fluoxetine (Prozac ), a serotonin-uptake inhibitor [53]. Using hydrogenation processes the functionalized amino ketones are converted directly into the respective products [8, 43e],... 

Charpentier-Morize and coworkers have developed conditions for the cycloalkylation of y-aryl-a-trifluoromethyl ketones selectively to either the cycloalkene (33) or the cycloalkyl chloride (34 Scheme 12) by varying the catalyst. 

Y-lMCtones Annulation of o-allyl aryl ketones to provide fused lactones by carbonylation under CO is observed in the presence of Cp2Ti(CO>2. 

Cyclopropanols undergo facile reaction with photoexcited aryl ketones such as benzophenone and fluorenone. Irradiation of fluorenone (14) and 1-phenylcyclopropanol gives a 78% yield of the coupling product 15. Spiro product 16, obtained from 1,2,2-trimethylcyclopropanol, may be derived from the y-hydroxy ketone by a further intramolecular cyclization reaction of this initial coupling adduct. 

Kawano Y, Togo H (2009) lodoarene-catalyzed one-pot preparation of 2,4,5-trisubstituted oxazoles from alkyl aryl ketones with mCPBA in nitriles. Tetrahedron 65 6251-6256 Jarikote DV, Siddiqui SA, Rajagopal R, Daniel T, Lahoti RJ, Srinivasan KV (2003) Room temperature ionic liquid promoted synthesis of 1,5-benzodiazepine derivatives under ambient conditions. Tetrahedron Lett 44 1835-1838... 

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