The Bingel reaction of the C(s) isomer of C(70)(CF(3))(8) has been found to yield two C(70)(CF(3))(8)[C(CO(2)Et)(2)] monoadducts and one C(70)(CF(3))(8)[C(CO(2)Et)(2)](2) bisadduct as its major products. Malonate addition occurs at those [6,6]-bonds that radiate from the polar pentagons of the C(70)(CF(3))(8) cage. Unexpectedly, X-ray single crystal analysis reveals dimerization of the above substances during crystallization, providing two isomers of {C(70)(CF(3))(8)[C(CO(2)Et)(2)]}(2), one isomer of {C(70)(CF(3))(8)[C(CO(2)Et)(2)](2)}(2) and {C(70)(CF(3))(8)}(2). This dimerization represents [2+2]-cycloaddition via [5,6]-bonds and results in functionalization patterns resembling several known C(70)X(10) derivatives.
Published data of the last 10 years concerning the development of new and upgrading of known approaches to indole synthesis are integrated and analyzed. Modern versions of the classical syntheses such as the Fischer synthesis, Nenitzescu synthesis, Ullmann reaction, Leimgruber – Batcho synthesis, Reissert synthesis, Bartoli reaction, Madelung synthesis and Cadogan – Sundberg reaction are considered. The presented new approaches include transformations of heterocycles, synthesis from o-alkynylanilines, reductive cyclization of nitrobenzene derivatives, synthesis with the use of arynes and catalysis by N-heterocyclic carbenes. The final Section summarizes original methods for the synthesis of indoles other than those listed above; they are classified in terms of the nature of the forming bond (C–C, C–N). Rarely used methods based on benzene ring construction in pyrrole derivatives are discussed separately.
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Employing DABCO as a substrate, aryl(mesityl)iodonium triflates are introduced as arylating agents for a tertiary sp 3 -nitrogen. Mild conditions and exceptional selectivity of the aryl group transfer allow unprecedented N-aryl-DABCO salts to be obtained, bearing substituents of different electronic natures. This metal-free methodology has no analogy among known transition-metal-based reactions. The utility of isolated N-aryl-DABCO salts is demonstrated for the preparation of flibanserin.
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