Indoles silver® fluoride

Conceptually it would be possible to prepare N-silylmethyliminium salts by the addition of an electrophile to the p carbon of N-silylmethylenamines [Eq. (5)]. The reaction of l-(trimethylsilylmethyl)indoles with silver fluoride is reported to be initiated by the addition of silver cation to the 3-position to form N-silylmethyliminium fluoride 44, whose desilylation by fluoride ion leads to azomethine ylides 45 (86JA1104). This is the only example known for the reaction depicted by Eq. (5). The narrow application of this method may arise from the lack of a general preparation for N-silylmethylenamines. 

A number of applications of the above-presented approach have been made in the synthesis of bicyclic amines. It has been used in the preparation of pyrrolo[l,2-a]indoles starting from N-trimethylsilylmethyl indoles, which are reacted with silver fluoride in an oxidation-reduction reaction to provide the desired products in good to excellent yields126 (equation 128). This same approach was applied to the preparation of some... 

Padwa and co-workers have continued their long standing studies in the area of azomethine ylide generation and trapping, and now report that the N-[(trimethylsilyl)methyl]indoles (102) react with the electron-deficient alkenes (103), in the presence of silver fluoride, to afford the cycloadducts (104) regio- and stereo-specifically.7 The azomethine ylide(105) is a probable... 

While most [3+2] cycloaddition reactions with indoles employ the indole moiety as the dipolarophile comptment, several reports have also highlighted the utility of indoles as the source of dipoles in 1,3-dipolar cycloaddition reactions. Padwa and coworkers produced early examples in which the indole pyrrole ring acted as an azomethine ylide dipole [94, 95]. Treatment of a silylated indole 235a with silver fluoride in the presence of a variety of dipolarophiles 236 and 238 afforded the corresponding cycloadducts 237 and 239 in 53% and 83% yield, respectively (Scheme 63). 

Using a 2-pyrimidyl directing group, indoles can be directly arylated with arylsilanes in aqueous media via a mild Rh-catalyzed process. The catalyst system consisted of [Cp RhCl2]2 with Cu(OAc)2 as an oxidant. Silver(I) fluoride was selected a fluoride source to activate the arylsilanes. Other fluoride sources, such as CsF and TBAF, showed no reactivity. Additionally, the reaction could be performed in water using THF as a cosolvent. Other arylsilanes could be employed, although... 

Silver(I) fluoride can also be used as a fluoride source. For example, a Cu-catalyzed orf/zo-fluorination process employing 8-aminoquinoline as an auxiliary was reported. Copper(I) iodide was chosen as the catalyst and NMO performed superiorly compared with other oxidants. A-methyl-protected indoles and pyridyl-derived carboxamides could be fluorinated in good yield (54 and 62%, respectively) however, the p)ridyl substrate required pyridine as a solvent to prevent product decomposition (eq 28). 

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