3- trimethylstannyl-indole

A solution of 1-tosyl-3-(trimethylstannyl)indole (500 mg, 1.15 mmol) in dry MeCN (20 mL) was stirred under N2 at rt. l-(Chloromethyl)-4-fluoro-l,4-diazoniabicyclo[2.2.2]octanebis(tetrafluoroborate) (F-Teda BF4, 6 500 mg, 1.15 mmol) was added in one portion and the solution stirred for 12 h. After 3 h a colorless precipitate began to appear. The mixture was filtered and the filtrate evaporated and purified by chromatography to give a colorless powder yield 70 mg (21 %) mp 87-88 C. 

Xenon difluoride is a better fluorinating reagent for vinyltin compounds than cesium fluoroxysulfate (compare entry 1 in Tables 1 and 2). Besides this, cesium fluoroxysulfate (which can be prepared from elemental fluorine and cesium sulfate) is known to be shock sensitive and to undergo detonation upon heating.26 27 However, cesium fluoroxysulfate is the alternative choice in the case of some vinyltin compounds, such as 2- and 3-(trimethylstannyl)indoles (Table 2, entries 5-7), whose reactions with xenon difluoride are not effective. 

The indolyltributylstannanes, which are more robust than their trimethylstannyl counterparts, are prepared similarly [166, 167]. Labadie and Teng synthesized the IV-Me, N-Boc, and jV-SEM (indol-2-yl)tributylstannanes [167], and Beak prepared the A-Boc trimethyl- and tributyltin derivatives in high yield [166]. Caddick and Joshi found that tributylstannyl radical reacts with 2-tosylindoles to give the corresponding indole tin compounds as illustrated [168]. 

The bromo derivative of A -mcthylsuccinimide did also undergo Suzuki coupling when treated with naphthylboronic acid in the presence of palladium acetate, triphenylphosphine and potassium carbonate (6.3.). The coupled product was deprotected under the reaction conditions and an indole derivative was isolated in good yield, which was successfully converted into the hexacyclic naphthopyrrolo[3,4-c]carbazole structure. Using the analogous trimethylstannyl-naphthalene derivative and optimised Stille coupling conditions the desired product was isolated only in 56% yield.5... 

The fluorination of 1-substituted indole 32 with F-Teda BF4 (6) in acetonitrile or acetonitrile/ methanol gives 3-fluoro-2-methoxy-l-tosyl-2,3-dihydroindole (33) in 48% isolated yield.87 Relative stereochemistry about the 2,3-bond in the dihydropyrrole ring was confirmed as trans by X-ray crystallographic analysis. F-Teda BF4 (6) reacts with 2- and 3-trimethylstannyl-sub-stituted 1-tosylindoles to give the corresponding fluoroindoles in 40 and 21 % yield, respectively.108... 

Indirect fluorination has been carried out using metallo-indoles. Hodgson et al used ipso substitution of 2- and 3-(trimethylstannyl)-l-(p-toluenesulfonyl)indoles. Of several fluorinating agents tried, cesium fluorosulfate was the best [43]. 5-Methoxyindoles lithiated in the 4-position were fluorinated by Wfluorobenzene-sulfonimide to prepare 4-fluoro analogs of serotonin and melatonin [44]. 

Analogous transformation with cesium fluoroxysulfate in the case of more electron rich l-methyl-2-(trimethylstannyl)-l/f-indole 24 leads to 2-fluoro-l-methyl-1/7-indole 25 in lower yield [8c],... 

Intermolecular homo coupling of alkenyltrimethylstannane functions provides a variety of other 8-trimethylstannyl a,p-unsaturated carbonyl compounds, as well as some corresponding allylic alcohols and selected structurally related analogs. A Pd(0)-Cu(l) bimetallic catalyst has been used in recent years for the synthesis of indoles from isocyanates and alkyl carbonates (eq 30). It is suggested that Cu(I) ions in this case probably act as 7r-coordinative Lewis acids. 

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