Indoles silver® acetate

In contrast with the relatively facile nucleophilic substitution reactions at the 2-position of the indole system, only 3-iodoindole has been reported to react with silver acetate in acetic acid to yield 3-acetoxyindole (59JOC117). This reaction is of added interest as 3-iodo-2-methylindole fails to react with moist silver oxide (72HC(25-2)127). It is also noteworthy that the activated halogen of ethyl 3-bromo-4-ethyl-2-formylpyrrole-5-carboxylate is not displaced during the silver oxide oxidation of the formyl group to the carboxylic acid (57AC(R)167>. 

There has been extensive reporting of the use of silver acetate for direct nucleophilic substitution. 3-Chloroindolenines react with silver acetate to give the product of direct displacement (eq 6). This is in contrast to reactions with softer nucleophiles (I , PhS , PO3) which give the parent indole. ... 

Methyl-2-diphenylphosphino-3-(l -isoquinolyl)indole with pallada-cycle derived from dimethyl-1-naphthyl ethylamine and potassium hexa-fluorophosphate yields chelate 310 (97T4035). With [(r)3-PhCH = CH = CHPh)Pd( j.-Cl)]2, allyl 311 follows in the presence of silver tetrafluor-oborate. Addition of ligands 312 (R = R1 = H, Me) to [(r 3-PhCHCHCHPh)Pd (Cl) ]2 under conditions of allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate leads to the formation of P,N-chelates 313 (R = R1 = H, Me), the active species of the catalytic reaction (00T(A)4753). 

Applications of this reaction are not limited to advanced materials, but can be applied to natural product synthesis. Indeed, indoles have quite recently (in 2008) been arylated in the presence of palladium acetate and silver oxide (Scheme 10.52).84... 

The regiochemical and stereochemical courses of the photocycloaddition of A-acylindoles with monosubstituted olefins such as methyl acrylate and vinyl acetate, as well as the possible mechanistic pathways for these reactions, have been the subject of several reports. In one of the earliest examples, the photocycloaddition of 1 -benzoylindole (8) and methyl acrylate (9) produced the compound 10, which was then converted via a short synthetic sequence to a variety of 2a,7b-dihydrocyclobut[h]indole derivatives 11 (Scheme 2). These compounds were in turn converted to the corresponding l//-l-benzazepines 12, through silver ion-catalyzed thermolysis reactions at 100-160°C [14, 15]. 

Intramolecular coupling reactions have also been performed via organometallic transformations where cesium acetate plays the role of a base. The direct lactonization of 2-arylacetic acids was performed in substantial 3ueld (75%) via a palladium catalyst in the presence of an oxidant, a 50/50 mixture of cesium and sodium acetate, and silver (I) acetate. Bis-indole alkaloids were also shown to be synthesized via intramolecular C-H insertion with palladium acetate and 2 equiv of cesium acetate in DMA in very high yield (94%). Substituted indoles have also been formed... 

Silver(I) acetate functions as an oxidant in the dehydrogenative cross-coupling of indoles and pyrroles with arenes. Whereas AgOAc favored C2 arylation for A-protected indoles, Cu(OAc)2 produced an inversion with selectivity, showing preference for C3 arylation (eq 29). Trace amounts of diarylated product were also detected. 

The direct oxidative C-phosphorylation of indoles with diallqrl phosphites in the presence of silver (I) acetate has been demonstrated by Wan et al. A wide variety of indoles and diallq l phosphites participated in the reaction to afford corresponding indolylphosphonates (225) in up to 71% yields (Scheme 75). ... 

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