Other organometallic reagents

There are a wide variety of methods for introduction of substituents at C3. Since this is the preferred site for electrophilic substitution, direct alkylation and acylation procedures are often effective. Even mild electrophiles such as alkenes with EW substituents can react at the 3-position of the indole ring. Techniques for preparation of 3-lithioindoles, usually by halogen-metal exchange, have been developed and this provides access not only to the lithium reagents but also to other organometallic reagents derived from them. The 3-position is also reactive toward electrophilic mercuration. 

Preparation of the appropriate optically active sulfmate ester is initially required for reaction with a Grignard or other organometallic reagent. If the method is to produce homochiral sulfoxides, the precursor sulfmate ester must be optically pure. An exception to this statement occurs if the reaction yields a partially racemic sulfoxide which can be recrystallized to complete optical purity. 

Nucleophilic 1,4- and 1,6-additions of cuprates and other organometallic reagents to acceptor-substituted dienes have been utilized extensively in target-oriented stereoselective synthesis52-61. Schollkopf and coworkers55 reported the diastereoselective 1,6-addition of a bislactim ether-derived cuprate to 3,5-heptadien-2-one (90% ds equation 17). The corresponding reactions of dienoates were conducted with the lithiated bislactim ether and proceeded with diastereoselectivities of >99% ds (equation 18)56 the adducts could be converted easily into diastereo- and enantiomerically pure amino acid derivatives. 

Distinction between PL and ET mechanisms is not straightforward. Various experimental methods have been used so far to demonstrate the ET process, including spectroscopic detection of radical intermediates detection of products indicative of radical intermediates " and measurement of secondary deuterium " and carbonyl carbon kinetic isotope effects (KlEs) "" . The combination of several experimental methods, including KIE, substituent effect and probe experiments, was shown to be useful in distinguishing the ET process from the PL process for the addition reactions of the Grignard and other organometallic reagents . 

OTHER ORGANOMETALLIC REAGENTS (see also Carbonylation, Fluorination, Reformatsky reaction) with acids and acyl derivatives with acid halides Benzylchlorobis(triphenyl-phosphine)palladium(II), 30 Cadmium, 60... 

OTHER ORGANOMETALLIC REAGENTS, with acids and acyl derivatives, with acid halides (Continued)... 

Lithium triethylborohydride (Super-Hydride) is a much more powerful reducing agent than lithium aluminium hydride. It is useful for the reductive dehalogenation of alkyl halides, but unlike lithium aluminium hydride does not affect aryl halides. It is available as solution in tetrahydrofuran in sealed containers under nitrogen. The solutions are flammable and moisture sensitive and should be handled with the same precautions as are taken with other organometallic reagents (see Section 4.2.47, p. 442). 

The synthesis of 2-methylbutanoic acid (Expt 5.129) is illustrative of the method. Other organometallic reagents undergo a similar carboxylation reaction, and examples of the use of organolithium and organosodium reagents are included in the section on the synthesis of aromatic carboxylic acids (Section 6.13.3, p. 1069). 

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