4-Acetylphenyl triflate

Furthermore, 4-acetylphenyl triflate could couple with alkyltrifluorosilane [Eqs.(30)] [26]. 

When (,S)-l-phenylethyltrifluorosilane of 34% ee was allowed to react with 4-acetylphenyl triflate (a), optically active 1-phenyl-l-(4-acetylphenyl)ethane was isolated. At 50 °C, almost complete retention of configuration resulted, but at higher temperatures the degree of retention dropped linearly and finally inversion resulted above 75 °C (a in Fig. 10-1). A similar temperature dependency was also observed in the case of 3-formylphenyl triflate (b) [30]. 

A significant solvent effect was observed. The reaction of 4-acetylphenyl triflate with PhCH(Me)SiF3 (38% ee, 5) at 60 °C resulted in retention (31% ee, S) in THF, but inversion (8% ee, R) in HMPA-THF (1 20). In DMF-THF (1 10) or DMSO-THF (1 10) retention (16% S in both cases) was still observed, but at a low level. Thus, in a nonpolar solvent, retention of configuration resulted, whereas in a polar solvent system the reaction proceeded by inversion [30]. 

The cross-conpling reaction of an optically active alkylsilane gives us valuable information on the stereochemistry in transmetallation. The reaction of (5)-l-phenyl-l-(trifluorosilyl)ethane (34% ee) with 4-acetylphenyl triflate in the presence of 5 mol % of Pd(PPh3)4 and TBAF (2 eqniv) at 50 C gave (5)-l-phenyl-l-(4-acetylphenyl)ethane of 33% ee with nearly complete retention of configuration. At higher temperatures, ee of the product decreased linearly, and above 75 °C inversion of configuration predominated (Scheme 26). Similar temperatnre dependency was observed also in the reaction of 3-formylphenyl triflate. 

Reactions were carried out using Pd(PPhj)4 (1.0 mmol) and 4-acetylphenyl triflate (112) (1.2 mmol) in DMF (5 mL). 

The alkyl-transfer process from tin to palladium causes the formation of methylarenes when ArSnMe, was used as the parent stannane, or K-butylarenes in the case of ArSnBu, usually in amount up to 30% [79]. Ordinarily preferential transfer of an aryl-over alkyl-group from tin to palladium became less favourable in the case of arylstannanes bearing coordinating substituents at the or//zo-benzylic positions. For example, the reaction of stannane 196 with 4-acetylphenyl triflate (197) gave the expected biaryl 198 in 50% yield, but also 4- -butylacetophenone (199) with a 24% yield [79], Scheme 30. 

Stille coupling of 4-acetylphenyl triflate proceeds rapidly with microwave irradiation. In the Stille reaction, the formation of minor amounts of 4-butylacetophe-none was encountered, which is formed frequently also on using standard heating procedures (Farina et al., 1993). 

Molander has recently reported the preparation of various 3-functionalized propyl trifluoroborates from the corresponding allyl derivatives following various literature protocols for hydroboration of alkenes [127]. The 3-heteropropyl trifluoroborates were obtained as crystalline air-stable solids by treatment of hydroboronated products with KHFj. Palladium-catalyzed cross-coupling of these 3-heteropropyl trifluoroborates with 4-acetylphenyl triflate gave functionalized alkylarenes in good yields (Scheme 3.82). 

The throughput of the system was subsequently doubled as a result of employing polymer-supported scandium triflate [PS-Sc(OTf)2] (79) as the Lewis acid catalyst, under the aforementioned reaction conditions. Using this approach, the authors demonstrated the generality of the technique, synthesizing a 10 x 5 array of a-aminonitriles, derived from 10 aliphatic and aromatic aldehydes and five amines. The chemoselectivity of the technique was also demonstrated using the reaction of 4-acetylbenzaldehyde (80) and 2-phenylethylamine (81) (Scheme 6.22) whereby 2-(4-acetylphenyl)-2-(phenethylamino)acetonitrile (82) was obtained, in 99.8% yield, as the sole reaction product. 

For performing the SM reactions of aryl mesylates, triflates, tosylates, and besylates, Percec s method involving Ni(dppf)Cl2 proved to be powerful and versatile alternative with moderate to good yields of biaryls. Thus the reaction of 4-acetylphenyl mesylate (295) with phenylboronic acid (260) resulted in 4-acetylbiphenyl (68) with a 51% yield [48], respectively. Scheme 32. 

IV-Phenylimidazolium triflate IV-Phenylimidazolium perchlorate 2-(Bromo)-4,5-(dicyano)imidazole IV-Methylbenzimidazolium triflate Pyridinium tetrafluoroborate IV-Methylanilinium trifluoroacetate lV-(p-Acetylphenyl)imidazolium triflate IV-Phenylimidazolium tetrafluoroborate ImidazoUum perchlorate 5-(/t-Nitrophenyl)-l//-tetrazole 4,5- (Dicy ano)imidazDle 4-(Phenyl)imidazDlium triflate Benzimidazolium tetrafluoroborate Imidazolium tetrafluoroborate Imidazolium triflate Benzimidazolium triflate 2-(Phenyl)imidazolium triflate A-Methylimidazolium triflate 4-(Methyl)imidazolium triflate l//-Tetrazole... 

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