Palladium-Catalyzed Tandem Alkenyl and Aryl C?N Bond Formation: A Cascade N-Annulation Route to 1-Functionalized Indoles

Diamine Ligands in Copper-Catalyzed Reactions

The utility of copper-mediated cross-coupling reactions has been significantly increased by the development of mild reaction conditions and the ability to employ catalytic amounts of copper. The use of diamine-based ligands has been important in these advances and in this review we discuss these systems, including the choice of reaction conditions and applications in the synthesis of pharmaceuticals, natural products and designed materials.

Recent advances in the synthesis of indole and quinoline derivatives through cascade reactions

Indoles and quinolines are ubiquitous structural motifs in many natural products and biologically active pharmaceuticals. The pursuit of synthetic efficiency has stimulated the design and development of new synthetic strategies to construct these heterocycles. One of the most effective ways of achieving efficiency is to implement reaction cascades, enabling multiple bond-forming and bond-cleaving events to occur in a single synthetic operation, thus circumventing the waste associated with traditional stepwise synthesis. In general, cascade reactions offer the opportunity to access highly functionalized final products from simple starting materials. For all these reasons, it is not a surprise that most of the recently reported methods for the synthesis of indoles and quinolines are based on the use of cascade reactions. In this Focus Review we discuss some of the most representative and interesting recent reports on the synthesis of indoles and quinolines through cascade reactions.

Room-temperature Pd-catalyzed amidation of aryl bromides using tert-butyl carbamate

The scope of Pd-catalyzed synthesis of N-Boc-protected anilines from aryl bromides and commercially available tert-butyl carbamate is described. For the first time, this process can be conducted at room temperature (17-22 degrees C) using a combination of Pd(2)dba(3).CHCl(3) and a monodentate ligand, tert-butyl X-Phos. Use of sodium tert-butoxide is crucial to the success of the reaction, which proceeds in 43-83% yield.

A general modular method of azaindole and thienopyrrole synthesis via Pd-catalyzed tandem couplings of gem-dichloroolefins

A palladium-catalyzed reaction of gem-dichloroolefins and a boronic acid via a tandem intramolecular C-N and intermolecular Suzuki coupling process gave corresponding substituted azaindoles or thienopyrroles. This method is a very modular protocol to synthesize all four isomers of azaindole and two isomers of thienopyrroles in good to excellent yield.

Assembly of Conjugated Enynes and Substituted Indoles via CuI/Amino Acid-Catalyzed Coupling of 1-Alkynes with Vinyl Iodides and 2-Bromotrifluoroacetanilides

Cross-coupling of 1-alkynes with vinyl iodides occurs at 80 degrees C in dioxane catalyzed by CuI/N,N-dimethylglycine to afford conjugated enynes in good to excellent yields. Heating a mixture of 2-bromotrifluoroacetanilide, 1-alkyne, 2 mol % of CuI, 6 mol % of L-proline, and K(2)CO(3) in DMF at 80 degrees C leads to the formation of the corresponding indole. This conversion involves a CuI/L-proline-catalyzed coupling between aryl bromide and the 1-alkyne followed by a CuI-mediated cyclization process. An ortho-substituent effect directed by NHCOCF3 enables the reaction to proceed under these mild conditions. Both aryl acetylenes and O-protected propargyl alcohol can be applied, leading to 5-, 6-, or 7-substituted 2-aryl and protected 2-hydroxymethyl indoles in good yields. With simple aliphatic alkynes, however, lower yields were observed.

Copper-Catalyzed Double N-Alkenylation of Amides: An Efficient Synthesis of Di- or Trisubstituted N-Acylpyrroles

An efficient copper-catalyzed double alkenylation of amides with (1Z,3Z)-1,4-diiodo-1,3-dienes is reported for the first time. The reactions proceed to afford di- or trisubstituted N-acylpyrroles in good to excellent yields using CuI as the catalyst, Cs2CO3 as the base, and rac-trans-N,N'-dimethylcyclohexane-1,2-diamine as the ligand.

Palladium-Catalyzed Functionalization of Indoles with 2-Acetoxymethyl-Substituted Electron-Deficient Alkenes

New functionalizations of indoles via palladium-catalyzed reaction of indoles and 2-acetoxymethyl-substituted electron-deficient alkenes are reported. It was found that for N-protected indoles the reaction proceeded smoothly in the presence of 5 mol % of Pd(acac)2 and 10 mol % of PPh3 at 80 degrees C in HOAc, while for N-unprotected indoles, the reaction was carried out by using 5 mol % of Pd(dba)2 or 2.5 mol % of Pd2(dba)3.CHCl3 with 10 mol % of 2,2'-bipyridine as the catalyst in toluene. This strategy allows the selective installation of electron-deficient olefin functionality at the 3-position of indoles, which might be difficult to obtain by other methods and can be further elaborated.

Tandem Palladium-Catalyzed Urea Arylation−Intramolecular Ester Amidation: Regioselective Synthesis of 3-Alkylated 2,4-Quinazolinediones

o-Halo benzoates can be combined with monoalkyl ureas in a tandem palladium-catalyzed arylation-ester amidation sequence to deliver quinazolinedione products. The reactions are regioselective for formation of the 3-N-alkyl isomers. Significant variation of both coupling partners is possible, allowing the synthesis of a diverse array of substituted quinazolinediones, exemplified by the preparation of a simple unsymmetric-dialkylated natural product. [reaction: see text]

Diversity Synthesis Using the Complimentary Reactivity of Rhodium(II)- and Palladium(II)-Catalyzed Reactions

Rhodium(II)-catalyzed reactions of aryldiazoacetates can be conducted in the presence of iodide, triflate, organoboron, and organostannane functionality, resulting in the formation of a variety of cyclopropanes or C-H insertion products with high stereoselectivity. The combination of the rhodium(II)-catalyzed reaction with a subsequent palladium(II)-catalyzed Suzuki coupling offers a novel strategy for diversity synthesis.

Zn(OTf)2-Catalyzed Cyclization of Proparyl Alcohols with Anilines, Phenols, and Amides for Synthesis of Indoles, Benzofurans, and Oxazoles through Different Annulation Mechanisms

Zn(OTf)2 (10 mol %) catalyzed the cyclization of propargyl alcohols with PhXH (X = O, NH) in hot toluene (100 degrees C) without additive and gave indole and benzofuran products with different structures. In such transformations, alpha-carbonyl intermediates A and C were isolated as reaction intermediates. The 1,2-nitrogen shift in the formation of indole is catalyzed by Zn(OTf)2, and its mechanism has been elucidated. This catalytic cyclization is also applicable to the synthesis of oxazoles through the cyclization of propargyl alcohols and amides without a 1,2-nitrogen shift.

n- and Isoalkane Adsorption Mechanisms on Zeolite MCM-22

Low-coverage adsorption properties (Henry constants, adsorption enthalpy, and entropy) of linear and branched alkanes (C3-C8) on zeolite MCM-22 were determined using the chromatographic technique at temperatures between 420 and 540 K. It was found that adsorption enthalpy and entropy of linear alkanes vary in a nonmonotonic way with carbon number. The adsorption behavior of alkanes was rationalized on the basis of the pore geometry. Short molecules prefer to reside in the pockets of the MCM-22 supercage, where they maximize energetic interaction with the zeolite. Longer molecules reside in the larger central part of the supercage. For carbon numbers up to six, singly branched alkanes are selectively adsorbed over their linear counterparts. This preference originates from the entropic advantage of singly branched molecules inside MCM-22 supercages, where these species have high rotational freedom because of their small length.

The Neber route to substituted indoles

Two complementary procedures have been developed for the conversion of the oximes of alpha-aryl ketones to azirines. On heating, the azirines rearrange smoothly to the corresponding indoles. The overall transformation offers a versatile route to indoles, complementary to the Fischer indole synthesis.

Synthesis of Lactams via Copper-Catalyzed Intramolecular Vinylation of Amides

Copper-catalyzed intramolecular vinylation of iodoenamides were investigated for the first time. With CuI as the catalyst and N,N'-dimethylethylenediamine as the ligand, a number of iodoenamides underwent cyclization in dioxane leading to the formations of five- to seven-membered lactams in moderate to excellent yields.