Alkyl Phenyl Ketone Branch

Other Six-membered Ring Syntheses.—Alkyl phenyl ketones possessing a branched alkyl chain of five or more carbon atoms undergo protolysis of a tertiary C—H bond on dissolving in the superacid HF-SbFs, producing carbonium ion intermediates which cyclize to 4,4-dialkyl-1-tetralones in good yield, e.g. (138)->(139) ... 

The substrate range - scope and limitations The reaction can be performed efficiently with a broad variety of ketone donors and aldehydes. Enantioselectivity, however, depends on the enolate structure (Scheme 6.11) [60, 61]. In general, eno-lates bearing larger, branched alkyl groups or a phenyl group result in lower enantioselectivity. The best results were obtained with enolates bearing a methyl substituent (product (S)-16, 87% ee) or a siloxymethyl substituent (product (S)-17, 86% ee). 

In general, //-alkyl, branched alkyl or phenyl acetylenic ketones are effectively reduced (Table 2), with the asymmetric induction usually being close to the enantiomeric purity of the a-pinene employed. 

Of the derivatives of p-phenylenediamine, the most effective are the N, N -di-alkyl derivatives, in which the alltyl possesses a branched hydrocarbon chain on the carbon closest to the nitrogen atom [235]. They are usually produced by reductive allq lation of p-nitroaniline, p-phenyl-enediamine, p-nitrodiphenylamine, p-nitrosodiphenylamine, or p-amino-diphenylamine with aldehydes and ketones [236-252] with hydrogen at a temperature of 100-250°C and a pressure from 5 to 200 atm in the presence of catalysts. Copper-chromium catalysts (mixtures of oxides of the metals chromium, copper, barium, etc.) [241, 242, 245-247, 249, 250], iodine in the presence of HCl, HBr, or HI [253, 254], Pt/C [245, 252], and Raney nickel [244] are most often used as the catalysts. 

The first iodine-catalyzed synthesis of 2-alkyl substituted oxazoles 130 by a decarboxylative domino reaction was reported. Aryl methyl ketones 128 were transformed in situ into a-iodo ketones and then, by the Kornblum oxidation, into 1,2-diketones. After the addition of the a-amino acid 129, an l2-mediated cyclization/decarboxylation gave oxazoles 130. The reaction proceeds better if the Ar has electron-donating substituents and if the R group is a branched alkyl chain or phenyl residue. The reaction used oxone to regenerate iodine (13JOC6065). 

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