3- indolenines

Better results have been obtained using the 3-(2-pyrrolidinylidene)indolenine intermediate 13.3A which can be prepared from indole-3-carboxaldehyde and pyrrolidine[16]. 

Few representative dyes of cyanine base (Table 2114) resulting from the condensation of alkylmercapto indolenine on 2-methylthiazoliurn have been described. 

The piC values of polymethine dyes depend on terminal group basicity (64) thus the protonation abHity diminishes if the basic properties of the residues decrease, passing from benzimidazole, quinoline, benzothiazole, to indolenine. On the other hand, the piC of higher homologues increases with chain lengthening. The rate constant of protonation is sensitive to other features, for example, substituents and rings in the chain and steric hindrance for short-chain dyes. 

Symmetrical, long-chain cyanine dyes for laser appHcations provide output from 680 to 980 nm (76). Although these dyes were obtained through early screening procedures, infrared dyes for other technologies use similar stmetures. A long-chain indolenine-type cyanine dye, general stmeture as in dye (34), has been described as the sensitizer in optical disk memories (77). 

Indoles. Indoles (89) are used as coupling components to give a2o dyes the stmcturaHy related indolenines (90) are also employed as intermediates in cyanine dyes. The arrows indicate coupling positions. In (89) R = H, aryl, alkyl = ryl, alkyl in (90) R, R = lyl) alkyl and R = alkyl. 

Reduction of indolenines with sodium and ethanol gives indolines. The pentachloropyr-role, obtained by chlorination of pyrrole with sulfuryl chloride at room temperature in anhydrous ether, was shown by spectroscopic methods to have an a-pyrrolenine (2H-pyrrole) structure (222). It is necessary, however, to postulate that it is in equilibrium with small but finite amounts of the isomeric /3-pyrrolenine form (3//-pyrrole 223), since pentachloropyrrole functions as a 2-aza- rather than as a 1-aza-butadiene in forming a cycloadduct (224) with styrene (80JOC435). Pentachloropyrrole acts as a dienophile in its reaction with cyclopentadiene via its ene moiety (81JOC3036). 

The condensation of a vinylogous formamide with an enamine has been applied to an aza azulene synthesis (351). The point of attachment of the aldehyde to the enamine in condensations with indolenin derived poly-enamines was found to favor the second double bond (352,353). 

The enamine-imine tautomerism of the indolenine system gives rise to rearrangement reactions of interest in indole alkaloid chemistry. Thus the synthesis of dihydroburnamicine (625) utilized the rearrangement of an acetoxyindolenine to an a-hydroxyalkyl indole, presumably through an intermediate enamine. Similarly 2,3-dialkyl indoles undergo oxidations to 2-acyl indoles (626-631). 

The arylhydrazone 29 of a 2-substituted cyclohexanone gave a mixture of indolenine 30 and tetrahydrocarbazole 30. It was reported that the relative amounts of 30 and 31 produced depended upon the catalyst employed. For example, glacial acetic acid as catalyst provided largely 30, whereas aqueous sulfuric acid gave 31 as the major product. 

Many 3-substituted indoles have also been prepared with the use of a-alkyl or a-aryl-p-keto sulfides. Thus indolization of aniline 5 with 3-methylthio-2-butanone 27 furnished indolenine 28, presumably via the same mechanism discussed earlier. The indolenine 28 was relatively unstable and reduced to the indole 29 without purification. Tetrahydrocarbazole 32 was prepared in 58% overall yield. Smith et al. made excellent use of the Gassman process in the total synthesis of (-i-)-paspalicine and (+)-paspalinine. ... 

Hoshino reported that a product, described as 3,3-dimethjd-indolenine (12), accompanied by some 1,3-dimethylindole (4) and a... 

In 1961 Acheson and Hands obtained 3-methyl-l-(2-nitroethyl)-indole (354) in low yield by the addition of nitrocthylene to 3-methyl-indole magnesium iodide. These authors also obtained 5-benzyloxy-l,3-bis(2-nitroethyl)iiidole (355) and 5,6-dimethoxy-3-(2-nitroethyl)-indolo (356) by the action of nitrocthylene on 5-henzyloxy- and 5,G-dimethoxyindolc magnesium iodide, respectively. They excluded the ]jossibility that the products 354, 355, and 356 had the isomeric indolenine structures on the basis of their absorption spectra and chemical properties. 

In the 19.S0 s a number of workers, including Hoshino, Oddo, and Kubota suggested that indolenine-type intermediates (cf. 431) were formed during the reaction of the indole Grignard reagents [depicted as N—MgX derivatives (cf. 432)] with alkyl and arylalkyl halides. Rather surprisingly these were the last reports dealing with... 

The reaction between phthalimidine (30) and triethyloxonium fluoroborate is reported to give the fluoroborate salt of 1-ethoxyiso-indolenine, from which the free base (35) can be liberated.The iso-indolenine (35) apparentlj shows no detectable tautomerism with the isoindole form (see Section IV, A). 

Isoindoles which have a free hlH group can undergo himolecular, oxidative coupling. Thus, 1-phenylisoindole (38), when refluxed in benzene in the presence of air, gives a 4,5% yield of the dehydrobisiso-indolenine (39), a product identical with that obtained by catalytic hydrogenation of o-cyanobenzophenone (37). ... 

Interest in this reaction was revived when the relevance of a carbene mechanism was realized, particularly following the demonstration (cf. SectionI,B) of a similar ring expansion of indene to 2-chloro-naphthalene by dichlorocarbene via the cyclopropane adduct. Indeed, at this time Nakazaki suggested that these reactions occurred by the addition of dichlorocarbene to the indolyl anion and subsequent rearrangement to the indolenine and, with loss of chloride ion, to the quinoline [Eq. (12)]. The preference of dichlorocarbene for... 

Under the conditions of the attempted conversion of the indolenine 17 into the quinoline 18 most of the indolenine was recovered, but there was also formed a small amount of a hydrolysis product, o-acetamido-jS-chloro-a-methylstyrene (22), obtainable in good yield with aqueous ethanolic potassium hydroxide. By analogy with a similar sequence of reactions in the carbocyclic series the hydrolysis product 22 might possibly undergo acid-catalyzed cyclodehydration to the quinoline... 

The reduction of 2-methyl-1,2,3,4-tetrahydro-y-carboline (92) with zinc and hydrochloric acid in the presence of mercuric chloride gives the indolenine derivative, 2-methyl-l,2,3,4,4a,9b-hexahydro-y-carbo-line (93). A related compound, 4,9b-diethyl-2-methyl-l,2,3,4,4a,9b-hexahydro-y-carboline (96), was obtained by catalytic hydrogenation of 95, which was prepared by Fischer ring closure of the phenyl-hydrazone 94. The stereochemistry of the B/C ring junction in these... 

Most of the substitution reactions of di-, tetra, and hexa-hydro-carbolines and of their oxo derivatives are similar to those of the parent indole or indolenine derivatives. Nitration and bromination of harma-line (l-methyl-3,4-dihydro-j8-carbolme) are referred to in Section IV, A, 1. Sulfonation and azO COupling ° proceed as expected for indole derivatives. The preparation of chlorinated and iodinated derivatives of 6-nitroharmaline has been reported,but their structures have not been established. 

A series of oxidative rearrangements of tetrahydro-j8-carbolines may be rationalized on the basis of a general reaction of 2,3-disub-stituted indoles which was recently recognized by Taylor. Attack at the 4a-position of the tetrahydrocarboline (341) by an electrophile yields the indolenine derivative 342, which is in equilibrium with the isomeric species 342a. Compounds of structure 342 and 342a can undergo a variety of reactions leading to different products. 

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