Palladium anisidine

The relay compound 1025 required for the synthesis of all of these 7-oxygenated carbazole alkaloids was obtained starting from commercially available 4-bromo-toluene (1023) and m-anisidine (840) in two steps and 72% overall yield. Buchwald-Hartwig amination of 4-bromotoluene (1023) with m-anisidine (840) furnished quantitatively the corresponding diarylamine 1024. Oxidative cyclization of 1024 using catalytic amounts of palladium(ll) acetate afforded 3-methyl-7-methoxycarbazole (1025). Oxidation of 1025 with DDQ led to clauszoline-K (98), which, on cleavage of the methyl ether using boron tribromide, afforded 3-formyl-7-hydroxycarbazole (99) (546) (Scheme 5.149). 

In 1998, a new type of Pd(II) binuclear complex was reported which was effective for Mannich reactions of an imine derived from glyoxylate and anisidine with silicon enolates [38,39]. In these reactions, use of solvents including a small amount of water was essential. It was shown that water played an important role in this system water not only activated the Pd(II) complex to generate a cation complex, but also cleaved the N-Pd bond of the intermediate to regenerate the chiral catalyst. This reaction reportedly proceeded via an optically active palladium enolate on the basis of NMR and ESIMS analyses. A unique binuclear palladium-sandwiched enolate was obtained in the reaction of the p-hydroxo palladium complex with the silyl enol ether [(Eq. (9)]. 

Kosak studied the hydrogenation of o-nitroanisole in details over palladium- and platinum-based catalysts at 95°C and 2.07 MPa H2.94 The hydrogenation of o-nitroanisole over palladium catalysts was always accompanied by the formation of o,o -hydrazoanisole, the amount of which varied significantly with different samples of starting o-nitroanisole. Impurities such as o-chloronitrobenzene and o,o -dichloroazoxybenzene present in o-nitroanisole were found to increase formation of the hydrazo compound with decrease in the yield of o-anisidine, while o-chloroanisole had no effect on the composition of the product. The hydrazo compounds were resistant to further hydrogenation under the conditions. Platinum-based catalysts were insensitive to the impurities and always gave o-anisidine of high purity. The results are summarized in eq. 9.46. 

Buchwald-Hartwig amination of p-bromotoluene with m-anisidine affords quantitatively the corresponding diarylamine. While oxidative cyclization using stoichiometric amounts of palladium(II) acetate provides only 36 % yield of 7-methoxy-3-methylcarbazole, up to 72 % yield is obtained using catalytic amounts of palladium(II). The highest turnover for the catalytic cycle is obtained with... 

Fierz-David and Ziegler (301) first applied this method to azo compounds. Ethyl acetoacetate and various aromatic amines (aniline, o- and p-toluidines, m-xylidine, o-anisidine, and chloroanilines) were convereted to acetoacetanilides and then coupled with diazotized sulfanilic acid. The azo dyes (38) were reduced with stannous chloride in hydrochloric acid to the corresponding aminoaceto-acetanilides (39), which in alkali formed the dihydropyrazines (40). Catalytic reduction of o-hydroxyphenylglyoxal phenylhydrazone in acetic acid over palladium has been shown also to give 2,5-bis(o-hydroxyphenyl)pyrazine (302). Reduction of chemical means has been shown to give... 

Clausine V (151) was prepared in two steps (Scheme 32) [150]. Buchwald-Hartwig coupling of /n-anisidine (113) with 3-bromoanisole afforded the diaryla-mine 150. Different reaction conditions have been tried for the subsequent palladium(ll)-catalyzed oxidative cychzation to clausine V (151) (Table 3). Application of 0.1 equiv. of palladium(ll) acetate and 0.1 equiv. of copper(ll) acetate in glacial acetic acid under an oxygen atmosphere gave the best result for the catalytic process (49% yield). The turnover number of almost 5 confirmed that the system works in a catalytic mode. However, in this case the best yield (67%) was obtained using stoichiometric amounts of palladium(ll) acetate in air without co-oxidant. 

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