Indoline from indole

Platinum oxide fluoroboric acid Indolines from indoles... 

Trimethylamine boranelhydrochloric acid Indoline from indole ring... 

Sodium trihydridocyanoborate acetic acid Indolines from indoles s. 31, 359... 

The Hegedus indole synthesis involves one of the earlier (formal) examples of olefin hydroamination. An ortho-vinyl or ortho-nllyl aniline derivative 1 is treated with palladium(II) to deliver an intermediate resulting from alkene aminopalladation. Subsequent reduction and/or isomerization steps then provide the indoline or indole unit 2, respectively. 

A novel approach to 3-substituted indolines and indoles via the anionic cyclization of 2-bromo-lV,lV-diallyanilines has been developed simultaneously by Bailey <96JOC2596> and Liebeskind <96JOC2594>. Thus, treatment of 2-bromo-lV,lV-diallylanilines 78 with 2 equivalents of BuLi at -78 °C leads to the formation of the intermediate 79 which may be trapped with an electrophile to afford 3-substituted indolines 80. Aside from ease of preparation, an additional benefit of the intramolecular carbolithiation of <7-lithio-W,Al-diallyl-anilines is the production of Al-allyl-protected indolines, which are easily deprotected using... 

The formation of 2-(indolin-2-yl)indole dimers from indole-3-acetic acid and its propyl ester in trifluoroacetic acid and phosphoric acid has been studied." The reaction involves electrophilic attack of the protonated species (24) on the free substituted indole to give the trans stereochemistry at the C(2)-C(3) bond. 

Indolines and indoles were prepared by a direct electrochemical reduction of arenediazonium salts. As a result, radical intermediates were generated from which 3,4-disubstituted tetrahydrofuran skeleta were constructed <02OL2735>. A short and stereoselective total synthesis of furano lignans was realized by radical cyclization of epoxides using a transition-metal radical source <02JOC3242>. Other preparations of tetrahydrofurans using radical cyclization include the synthesis of novel amino acids L-bis-... 

Indolines can be obtained easily from indoles by reduction (see 20.7) and can be cleanly oxidised back to indoles nsing a variety of methods, including oxygen with cobalt catalysis (salcomine), hypochlorite/ dimethyl snlhde, Mn(lll) and An(lll) compounds, DDQ or manganese dioxide. ... 

Photoexcited acetone has been used previously to generate aromatic compounds from dihydroaromatic compounds by hydrogen abstraction. Further studies14 have revealed the limitations of this procedure, and shown that other products are often formed from ketyl and hydroaromatic radical coupling. Only the conversion of indoline into indole occurs in reasonable yield (46%). Hydrogen abstraction by excited acetone also appears to be responsible for an unusual reaction on irradiation of friedelin (13) in ether-acetone.16 The known intramolecular reaction which occurs in the cyclohexanone ring gives a keten (Scheme 2), but this is followed by addition of a ketyl radical and subsequent reduction to produce an hydroxycarbonyl compound (14). 

The third method involves the formation of ring carbon starting from indole or indoline derivatives. 

From a synthetic point of view, indolines are used to provide different reactivity properties from the indoles. Once a required sequence of reactions is achieved, the indoline can then be oxidized readily to the indole. One of the most effective methods for the conversion of indolines to indoles involves treatment with benzeneseleninic anhydride, together with three equivalents of a sacrificial scavenger such as indole or dihydropyran to remove the phenylselenating by-product the method has been used in the synthesis of ergot alkaloids (Equation (100)) <85TL4183, 90JCS(pi)707>. 

This reaction can be traced back to the initial work of Cadogan for the preparation of car-bazole by the reductive cyclization of aromatic nitro compounds with triethyl phosphite. This reaction was then extended by Sundberg to the fornnation of indoles by the treatment of o-nitrostyrene with triethyl phosphite or the formation of indolines from the o-alkyl nitrobenzenes. Thus the formation of indole from the reduction of o-nitfostyrenes is referred to as the Cadogan-Sundberg indole synthesis." ... 

A number of other indoline-to-indole dehydrogenations are known, although they have received lesser attention from the synthetic community compared to the previous methods. 

Bereman and Nalewajek (72) described the synthesis of dithiocarbamates derived from indole, indoline, carbazole, and imidazole (Fig. 7). Again, the amides are initially generated in dry THF upon addition of potassium metal, and later addition of excess carbon disulfide at —78°C leads to generation of the potassium salts of the dithiocarbamates (Eq. 4). While the indoline and imidazole derivatives are relatively air stable, the others are extremely air sensitive decomposing in a matter of minutes. The potassium salt of the dithiocarbamate derived from 2,2 -dipyridylamine (Fig. 7) has been prepared in a similar fashion, and while air stable, it is extremely hygroscopic (73). 

Indol-3-ylcarbinols can also be reduced using Et3SiH-TFA. Aryl indolyl-3-ylcarbinols can be formed in situ from 2-alkylindoles and benzaldehydes. These reactions, when run in tandem, provide a versatile route to 3-benzylin-doles[l 1]. Indole itself undergoes reduction to indoline under these conditions. lndol-3-ylcarbinols can also be generated by organomelallic additions to 3-acylindoles[12]. 

Indole and indoline alkaloids —C(0)(CH2)4C02CH3 from dimethyl adipate (CH30C(0)C=CHC(0)CH3)... 

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