Indolenines reduction

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 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... 

The synthesis reported by Bonjoch and co-workers utilizes a Ni-mediated reductive cyclization of vinyl iodide 82 with concomitant reductive indolenine formation quenching of the presumed intermediate (dehydrotubifoline, 83) with the Vilsmeier reagent affords A-formyl derivative 84 [36b]. Photoisomerization gives norfluorocurarine (22) in low yield. Similarly, Rawal and He produce... 

The second method leads to the formation 3-alkyl- and 3-arylindoles from the reaction of indole with aldehydes in the presence of alkali metal tetra-carbonylhydridoferrate (Scheme 40).67 It is possible that this novel process may occur via reduction of intermediate 3-alkylidene- or 3-arylidene indolenines. 

Compound 172 exhibited typical indolenine UV absorptions and mass Spectral fragmentation very similar to those of 15,20-anhydrocapuronidine (303), obtained by concentrated H2S04 dehydration of 170. Upon reduction with NaBH4, the indolenine 172 was converted to its 1,2-dihydro derivative, identical to the natural product 173. Catalytic hydrogenation gave a tetrahydro derivative, characterized by a peak at m/z 190 in the mass spectrum, typical of pseudoaspido-spermatane alkaloids. 

As a further illustration of the reactivity of the 3 position toward electrophiles, the methoxyindole (25-1) readily undergoes Mannich reaction with formaldehyde and dimethylamine to afford the aminomethylated derivative (25-2). Treatment of that intermediate with potassium cyanide leads to the displacement of dimethylamine and the formation of the nitrile (25-3), possibly by an elimination-addition sequence involving a 3-exomethylene-indolenine intermediate. The protons on the methylene group adjacent to the nitrile are quite acidic and readily removed. Reaction of (25-3) with methyl carbonate in the presence of sodium methoxide gives the carbo-methoxylated derivative (25-4). Catalytic hydrogenation leads to reduction of the nitrile to a primary amine. There is thus obtained the antihypertensive agent indorenate (25-5) [26]. 

Polyisoindolenines, which are high-molecular Phthalogen developers and are complexes of heavy metals and indolenine, are developed with reducing agents in a wet treatment. The polyisoindolenine complexes are fiber-affinitive and can be applied by using the exhaustion process. Their substantivity is low but can be increased by pretreating the cellulose with anionic products. Reductive development is performed in an alkaline medium with hydrosulfite. For details, see [82, 83],... 

Cerutti and Schmid105 employed the principles of metal hydride reduction as a structural confirmation for the products obtained from the photo-reduction of a series of indolenine type compounds. The reduction product of 9,4a-diethyld,2,3,4-tetrahydrocarbazolinium chloride (95) with sodium borohydride was found to be identical with the photo-reduction product obtained from mercury sensitized irradiation of 95, confirming the structure of the product as 96. 

The indolenine (232) has been neatly used in a synthesis of ( )-strempeliopine (233), the laevorotatory enantiomer of which has recently been isolated from Strempeliopsis strempelioides K.. Schurn.108 Reductive rearrangement of (232) by... 

It is a good solvent for both naphthostyrile (1) and lithium aluminum hydride, and proved useful for the reduction of (1) to benz(cr/)indolenin (2)." A solution of 1 g. of (1) in 20 ml. of N-ethylmorpholine was stirred with exclusion of air and treated at 50-60° with 0.5 g. of l.iAIH,. The solution turned green and then fluorescent blue, and after 1.5 min. the mixture was hydrolyzed carefully w th water and worked up. 

The enantioselective approach to quebrachamine adopted by Fuji and collaborators (Scheme 41) (279) has also been modified to afford a new synthesis of (-)-aspidospermidine (251). Here, the lactone 446 was converted by titanium trichloride into the lactone hemiacetal 485, which, after appropriate reduction and oxidation stages, gave the acetal acid 486. Condensation with tryptamine gave the tetracyclic lactam 487, which was then rearranged by means of trifluoromethanesulfonic acid to the pentacyclic indolenine lactam 488, reduction of which gave (-)-aspidospermidine (251) (Scheme SI). 

Transannular cyclization. In a recent total synthesis of indole and dihydroindole alkaloids,3 a key step is a transannular cyclization reaction with mercuric acetate. For example, the reaction of 4/3-dihydrocleavamine (1) with mercuric acetate yields the indolenine (2), which was isolated as the more stable reduction product (3). 

Reduction with formic acid50 provides a way of cleaving the C(21)—C(7) bond (Scheme 15) in (— )-vincadifformine (40b) and (— )-tabersonine (40c) previously it was necessary to remove the ester group and reduce the resulting indolenine (for example as above). Formic acid is unique in providing of itself both a proton, to produce a concentration of indoleninium cation (43), which in... 

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