Indole-2-carboxylate complexes

Enantioselective additions of a,f)-unsaturated 2-acyl imidazoles, catalyzed by bis(oxazolinyl)pyridine-scandium(III)triflate complex, were used for the asymmetric synthesis of 3-substituted indoles. The complex 114 was one of the most promising catalysts. The choice of acetonitrile as the solvent and the use of 4 A molecular sieves were also found to be advantageous. The 2-acyl imidazole residue in the alkylation products of u,(i-unsaturated 2-acyl imidazoles could be transformed into synthetically useful amides, esters, carboxylic acid, ketones, and aldehydes (Scheme 32) [105]. Moreover, the catalyst 114 produced both the intramolecular indole alkylation and the 2-substituted indoles in good yield and enantioselectivity (Scheme 33) [106]. The complex... 

Rh2(II)-carboxylate complexes have been reported to promote the selective migration of aminomethylenes in )5,)5-disubstituted styryl azides to form 2,3-disubstituted indoles with stepwise migration before diffusion of the iminium ion (Scheme 155). ... 

A traditional method for such reductions involves the use of a reducing metal such as zinc or tin in acidic solution. Examples are the procedures for preparing l,2,3,4-tetrahydrocarbazole[l] or ethyl 2,3-dihydroindole-2-carbox-ylate[2] (Entry 3, Table 15.1), Reduction can also be carried out with acid-stable hydride donors such as acetoxyborane[4] or NaBHjCN in TFA[5] or HOAc[6]. Borane is an effective reductant of the indole ring when it can complex with a dialkylamino substituent in such a way that it can be delivered intramolecularly[7]. Both NaBH -HOAc and NaBHjCN-HOAc can lead to N-ethylation as well as reduction[8]. This reaction can be prevented by the use of NaBHjCN with temperature control. At 20"C only reduction occurs, but if the temperature is raised to 50°C N-ethylation occurs[9]. Silanes cun also be used as hydride donors under acidic conditions[10]. Even indoles with EW substituents, such as ethyl indole-2-carboxylate, can be reduced[ll,l2]. 

Melanin biosynthesis in animals is a complex process starting with the L-tyrosine amino acid. In the first step, L-tyrosine is converted first into DOPA and then into dopaquinone, a process catalyzed by tyrosinase. In the biosynthesis of eumelanins, dopaquinone undergoes a cyclization to form dopachrome and subsequently a tau-tomerization into 5,6-dihydroxyindole-2-carboxylic acid (DHICA). DHICA is further oxidized to indole-5,6-quinone2-carboxylic acid, the precnrsor of DHICA eumelanins. Tyrosinase-related proteins TRP-2 and TRP-1, respectively, are responsible for the last two steps, and they are under the control of the tyrosinase promoter. 

The higher acidity of pyrroles and indoles bearing electron-withdrawing substituents at the a- or /3-positions permits their alkylation under mildly basic conditions, but although the thallium salt of 2-formylpyrrole is Af-alkylated, the corresponding alkylation of the thallium salts of ethyl pyrrole-2-carboxylate yields a complex mixture of products resulting from iV-alkylation and transesterification (B-77MI30502). N-Alkylation of pyrrolyl and indolyl esters is most conveniently effected under phase-transfer conditions. 

Rate and equilibrium constants have been reported for the reactions of butylamine, pyrrolidine, and piperidine with trinitrobenzene, ethyl 2,4,6-trinitrophenyl ether, and phenyl 2,4,6-trinitrophenyl ether in acetonitrile, hi these reactions, leading to cr-adduct formation and/or nucleophilic substitution, proton transfer may be rate limiting. Comparisons with data obtained in DMSO show that, while equilibrium constants for adduct formation are lower in acetonitrile, rate constants for proton transfer are higher. This probably reflects the stronger hydrogen bonding between DMSO and NH+ protons in ammonium ions and in zwitterions.113 Reaction of 1,3,5-trinitrobenzene with indole-3-carboxylate ions in methanol has been shown to yield the re-complex (26), which is the likely precursor of nitrogen- and carbon-bonded cr-adducts expected from the reaction.114 There is evidence for the intermediacy of adducts similar to (27) from the reaction of methyl 3,5-dinitrobenzoate with l,8-diazabicyclo[5.4.0]undec-8-ene (DBU) cyclization eventually yields 2-aminoindole derivatives.115... 

In a sequence of complex reactions, which will not be considered in detail, the indole ring system is formed by incorporating two carbons from phosphoribosyl diphosphate, with loss of the original anthranilate carboxyl. The remaining ribosyl carbons are then removed by a reverse aldol reaction, to be replaced on a bound form of indole by those from L-serine, which then becomes the... 

Thus, the hydrodesulfurization process is a very complex sequence of reactions due, no doubt, to the complexity of the feedstock. Furthermore, the fact that feedstocks usually contain nitrogen and oxygen compounds (in addition to metal compounds) increases the complexity of the reactions that occur as part of the hydrodesulfurization process. The nitrogen compounds that may be present are typified by pyridine derivatives, quinoline derivatives, carbazole derivatives, indole derivatives, and pyrrole derivatives. Oxygen may be present as phenols (Ar-OH, where Ar is an aromatic moiety) and carboxylic acids (-C02H). The most common metals to occur in petroleum are nickel (Ni) and vanadium (V) (Reynolds, 1997). 

Decarbonylation decarboxylation. At 110-170° this complex in catalytic amounts effects decarbonylation of simple aldehydes in quantitative yield.- Decarbonylation of typical indole-2-carboxaldehydes with in j/ M-generated catalyst proceeds in 82-95% yield. In fact, decarboxylation of some indole-2-carboxylic acids can be effected in higher overall yield by conversion to the aldehyde (LiAlH4 MnO,) followed by decarbonylation than by copp)er-catalyzed decarboxylation. ... 

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