Racemic 4-substituted indole

Methyl trifluoropyruvate alkylates a series of substituted indoles catalysed by the chiral non-racemic 2,2/-bipyridylcopper(II) triflate complex (32) to form methyl 3,3,3- trifluoro-2-hydroxy-2-indole-3-yl propanoates [e.g. (33)] in high enantiomeric excess and good yield.37... 

Racemic entry to quaternary C3 hydroxy oxindoles from C3-substituted indoles has been achieved using a variety of oxidants including dimethyldioxirane [56], CeCl3 7H20/IBX [57], or PCC (pyridinium chlorochromate) with polyaniline salt (PANl) as acid catalyst [58]. 

Regioselective C-H activation is often used for intramolecular biaryl preparations in Pd-mediated transformations. Thus concise syntheses of a large collection of alkaloids have been reported using variations of this approach (239-241), which differ mainly in terms of the functionalization of the precursor, palladium catalysts, and ligands. An efficient synthesis of racemic y-lycorane was recently disclosed whereby the key step is the intramolecular a-arylation of a cyclohexanone derivative (242). Some heterocycKc synthetic precursors (e.g. substituted indoles, quinolines, quinolones, phenanthridines, and phenanthridinones) have also been prepared en route to the alkaloids [hippadine, trisphaeridine (70), and crin-asiadine] via Pd- and Cu-mediated reactions (243,244). 

You and coworkers employed 4,7-dihydroindoles 79 instead of indoles 75 in the Friedel-Crafts reaction with nitroalkenes 77 (Scheme 11.22) [41]. Catalyst Ig with a 9-anthryl group displayed excellent performance. The notable point in this reaction is the use of the syringe pump technique to achieve high enantioselectivities and suppress the background reaction. Subsequent oxidation of Friedel-Crafts adducts 80 by p-benzoquinone afforded 2-substituted indole derivatives 81 in excellent yields without racemization. This approach and the simple asymmetric Friedel-Crafts reaction of indoles are complementary methods for obtaining the different substitution patterns of chiral indole derivatives. 

Since tryptophan synthase does not (or poorly) tolerate the substitution of indoles by large groups (iodo- and nitro-groups), such cases have lead to the development of a facial chemical synthesis of racemic A-oc-acetyltryptophan derivatives from 5- and 6-monosubstituted indoles and L-serine, followed by an enzymatic resolution step using acylase Amano resulting in substituted L-tryptophans in high yields and enantiomeric purity of 91-100% ee [66] (Fig. 4). 

A number of substituted benzenes, naphthalenes, indans, pyridmes, and indoles form arene(tricarbonyl)chromium complexes upon thermolysis under an inert atmosphere, usually in a high boiling ether, or by irradiation of the arenes in the presence of chromium hexacarbonyl. The complexes are relatively air-stable and can usually be stored for long periods in the absence of light. Somewhat milder conditions can be used by transfer of the chromium tricarbonyl group from preformed naphthalene(tricarbonyl)chromium, tris(L)tricarbonyl chromium (L = acetonitrile, ammonia, pyridine), or tricarbonyl( -l-methylpyrrole)chromium. Enan-tiomerically pure arene(tricarbonyl)chromium complexes having two different substituents, either ortho or meta can be prepared conveniently by classical resolution of racemic... 

Certain plants of the Rutaceae produce a number of different coumarin dimers in which the monomeric units, an isopentadienyl-substituted coumarin, are joined in a Diels-Alder fashion. The structural features resulting from this mode of dimerization are not restricted to coumarins in the Rutaceae but can also be found in two sets of dimeric 2-quinolones, indole alkaloids and related isopentenyl substituted compounds. A remarkable feature of all of these dimers is that they occur as racemates in spite of the fact that they all have two or more asymmetric centers. The racemic nature of these coumarin dimers has raised the possibility that these substances might arise by a non-enzymatic Diels-Alder reaction during biosynthesis. 

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