Phenyl 1-alkenyl ketones

Hydroborations of enortes. Phenyl 1-alkenyl ketones arc reduced by 9-BBN or catecholborane (CB) (1 equiv.) in >95% yield to boron (Z)-cnolalcs (>99/1), irrespective of the substituents on the alkenyl group. The reaction is more rapid with... 

Table 6.29 Hydroboration of phenyl 1-alkenyl ketones (1) with 9-BBN and catecholborane [14]...

Table 20.7 Hydroboration of phenyl-1 -alkenyl ketones with 9-BBN [16] ...

On the contrary, the arrangement is dominated by electronic effects because of 7r-7r-interactions between the axial 0-Al and the substituents of the ketone. Repulsive interactions that occur with r-systems of unsaturated groups such as phenyl, alkenyl or alkynyl make these groups large... 

A variety of substituents—including alkyl, alkenyl, cyano, acetyl, and alkoxy— is tolerated at the 2 and 5 positions of the oxazole ring for these cycloadditions. Acetylenic dienophiles with alkyl, trialkylsilyl, phenyl, ester, ketone, and acetal substituents, as well as terminal alkynes, are precedented. Ab initio calculations predict a slightly higher activation energy for the cycloaddition of oxazole with acetylene compared to the oxazole-ethylene reaction. ... 

The boron (Z)-enolates (>99%, Z), prepared by 1,4-addition of 9-BBN or catecholborane to phenyl-1-alkenylketones, are converted to trimethylsilylenol ether by treatment with methylmagnesiumbromide at -78 °C and then with chlorotrimethylsilane. On the other hand, protonolysis of (Z)-enolates afford 1-phenyl-1-alkanone (Scheme 6.30) [14]. The high selectivity-forming boron enolate is not observed in the reaction of catecholborane or 9-BBN with alkyl alkenyl ketones [15]. 

The dienone 858 is synthesized by coupling of the alkenyl copper reagent 856 with crotyl chloride (857) in the presence or absence of ZnCl2[731], Tetrabutyllead (859) reacts with benzoyl chloride to afford butyl phenyl ketone[732]. 

This chemistry was extended to a catalytic enantioselective alkenylation and phenylation of aldehydes and a-ketoesters. Using CuF-DTBM-SEGPHOS complex, products were obtained with excellent enantioselectivity from a wide range of aldehydes including aromatic and aliphatic aldehdyes, [Eq. (13.26)]. Previously catalytic enantioselective vinylation and phenylation are restricted using the corresponding zinc reagents. The active nucleophile is proposed to be an alkenyl or phenyl copper, based on NMR studies. The chiral CuF catalyst can also be applied to a catalytic enantioselective aldol reaction to ketones... 

Trifluoromethyl ketones have been alkenylated, alkynylated, and phenylated in high ee using silane reagents and a chiral copper(I)-diphosphine complex.178... 

Noyori et al. proposed that the reaction would be initiated by complexation of the Lewis acidic lithium cation to the ketone oxygen atom then hydride transfer occurs from aluminum to the carbonyl carbon by way of a six-membered chairlike transition state3 (Scheme 4.3c). Between the two competing six-membered chairlike transition states A and B, transition state B is disfavored, due to the substantial n/it-type electronic repulsion between the axially oriented binaph-thoxyl oxygen and the unsaturated phenyl or alkenyl moiety. Although there is a 1,3-diaxial steric interaction between the Al-0 and C-R bonds in transition state... 

Alkenyl halides and aromatic halides are unreactive with ketones in the presence of Sml2 in THF. Pinacolic coupling products can be detected in 10-20% yield under these conditions. In THF/HMPA, io-dobenzene reacts in the presence of a ketone to generate a phenyl radical, which abstracts a hydrogen from THF. Samarium diiodide induced coupling of the THF radical to the ketone (or ketyl) provides the major observed product (equation 21). ... 

The same general methodology applied to the preparation of alkenyl(silyl)cyclopropanes (vide supra) was previously developed for preparing alkenyl(sulfanyl)cyclopropanes. In this method, the lithium derivative of cyclopropyl phenyl sulfide (1) was used to alkylate a ketone and the resulting tertiary alcohol 2 was then dehydrated to give the product... 

Alkylation of symmetrical ketones or of ketones that can enolize in one direction only can, of course, give just one mono-C-alkylated product. With unsynametrical ketones, however, two different monoalkylated products may be formed by way of the two structurally isomeric enolate anions. If one of the isomeric enolate anions is stabilized by conjugation with another group, such as cyano, nitro or a carbonyl group, then only this stabilized anion is formed and alkylation takes place at the position activated by both groups. Even a phenyl or an alkenyl group provide sufficient stabilization of the resulting anion to direct substitution into the adjacent... 

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