Phenyllead triacetate

In order to determine whether or not these and similar reactions proceed through radical species, 2-(3,3-diphenylprop-2-enyloxy)phenyllead triacetate, a compound containing an internal radical trap, was prepared, and its behavior in base-catalyzed C-arylation reactions investigated. The absence of benzofuran derivatives among the products excluded the participation of radical species in these processes.35... 

Reactions of aryllead triacetates with olefins (Heck-type reactions) proceed similarly but do not require Cul as co-catalyst. From the numerous reported reactions, that of phenyllead triacetate with 2,3-dihydrofuran is mentioned as a typical example. This affords the C-C coupling product 27 in 68% yield, together with 10% of the homocoupling product (Equation (ll)).47... 

Menendez et al. reported the synthesis of murrayafoline A (7) by palladium(II)-mediated oxidative double C-H activation of a diarylamine assisted by microwave irradiation (585). The aniline derivative 598 was obtained by O-methylation of 5-methyl-2-nitrophenol (625) followed by catalytic hydrogenation. The required diarylamine 654 was obtained by N-arylation of the aniline derivative 598 with phenyllead triacetate (653) in the presence of copper(II) acetate. Under microwave-assisted conditions, in the presence of more than the stoichiometric amount of palladium(II) acetate and a trace of dimethylformamide, the diarylamine 654 was cyclodehydrogenated to murrayafoline A (7) (585) (Scheme 5.47). 

Recently, redistribution reactions between phenyllead compounds have been used to prepare triphenyllead chloride from tetraphenyllead and diphenyllead dichloride 202>, and, using mercury acetate in acetic acid as a catalyst, phenyllead triacetate from diphenyllead diacetate and lead tetraacetate, and diphenyllead diacetate from tetraphenyllead and lead tetraacetate 325>. The mercury acetate catalyst is notable in that it does not catalyze the redistribution of alkyllead compounds. 

However, it requires rather hindered /3-ketocstcrs to observe a significant drop in the yield of the arylation reaction with />-rn ethoxy phenyl lead triacetate 1 (Equation (3)).16 On the other hand, if the /3-dicarbonyl moiety is inserted into a cyclic structure, this difference disappears. For example, in the synthesis of functionalized tetramic acid derivatives, reaction of phenyllead triacetate 2 with the two five-membered cyclic pyrrolidinediones 3 and 4 afforded the diphenyl derivative 5 with a similar efficiency of the arylation step (Equations (4) and (5)).17... 

In general, the rate of the reaction of arylation of phenols by aryllead triacetate increases with the electron density of the phenolic substrate. When pyridine is used as a base, no reaction takes place with electron-poor phenols, such as 2,6-dichlorophenol or 2,6-dichloro-4-nitrophenol.45 45a However, the reaction of the sodium salt of perfluorophenol 43 with phenyllead triacetate under more forcing conditions led to a range of products the product of >rtfe -arylation, the 6-aryl-2,4-cyclohexadienone 44 together with minor amounts of the product of / zra-arylation 45 and the unsymmetrical diaryl ether 46 (Equation (43)).69... 

Barton, D. H. R., Yadav-Bhatnagar, N., Finet, J. P., Khamsi, J. Phenylation of aromatic and aliphatic amines by phenyllead triacetate using copper catalysis. Tetrahedron Lett. 1987, 28, 3111-3114. 

The palladium-catalyzed coupling reactions of organolead triacetates with olefins have been achieved under mild conditions [53]. Phenyllead triacetate undergoes facile coupling with the diol olefin without any formation of ketone resulting from -PdH elimination to give the arylated diol (Scheme 13.30). The use of NaOMe as a base is critical in this type of coupling. 

However, under more forcing conditions, high yields of the 2,6-diaryl derivatives (46) can be obtained, and particularly with more reactive aryllead derivatives, such as 2,4,6-trimethoxy-phenyllead triacetate (48). 12 Highly hindered structures of the 2 -hydroxy-r,3 -terphenyl type can be obtained. For example, 3,5-di-re/t-butylphenol (47) reacts with 2,4,6-trimethoxyphenyllead triacetate (48) to afford the very sterically hindered 2,6-diarylphenol (49) in 87% yield. 125,126... 

Ph] was obtained in 91% by phenylation of 5-ethylbarbituric acid [(73), R = Et] with phenyllead triacetate. However, in sharp contrast, the 5-unsubstituted barbituric acid behaved like dimedone to give good yields of the product of diarylation (55-61% with 2 equivalents of aryllead triacetate). 

The a-phenylsulfonylketone analogues reacted similarly with aryllead triacetates to yield the corresponding a-aryl derivatives in good yields (69-74%) except in the case of 2,4,6-trimethoxy-phenyllead triacetate with which no reaction took place. 

The preparation and reaction of zincated quinolines offers an effective means for substitution <97T7237>. The copper-mediated coupling of l,2-dihydroquinolin-2-ones with phenyllead triacetate was studied. Depending on the sub.stitution of the ring the regiochemistry varies between the 1- and 3-positions or both <97JCS(P1)229>. 

Dibenzo[W]pyrans are formed when o-(bromomethyl)phenyllead triacetates are heated with phenols (Scheme 14) <01TLS875>. Fused dibenzo -pyrans and -thiopyrans result from the cycloaromatisation of the non-conjugated tetraynes 15 (Scheme 15) <01H(54)887>. 

Diaryls. Trifluoroacetic acid added to a mixture of mesitylene and p-fluoro-phenyllead triacetate product. Y 88%. F. e., limitations, and reactions s. H. C. Bell et al., Tetrah. Let. 1974, S57, 853. 

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