Rhodium-Catalyzed Cross-Coupling Reactions

Rhodium-Catalyzed Cross-Coupling Reactions 4.1 Selective C2-Arylation... 

A very large number of indole-based hgands have been developed to facihtate palladium- and rhodium-catalyzed cross-coupling reactions. The research groups of Sannicolo, Benincori, Beller, Reek, Koskinen, Heo, Mino, Sarkar, Franzen, and Kwong have made enormous contributions in this area. 

Scheme 4.61 Ni-catalyzed cross-coupling of arylzinc halides with a-bromoglycosides [207]. 4.5.1.3 Rhodium-Catalyzed Cross-Coupling Reactions...

Wang, J., Liu, B., Zhao, H., Wang, J. (2012). Rhodium-catalyzed cross-coupling reactions of carbox-ylate and organoboron compounds via chelation-assisted C-C bond activation. Organometallics, 31, 8598-8607. 

A rhodium-catalyzed cross-coupling reaction of 8-quinlinyl ketone 21 with arylboronic acid, was reported to deliver 8-aroylquinoline 22 (Scheme 6.6) [14]. 

In Chap. 6, a companion to the preceding chapter, Li and Gribble document Metal-Catalyzed Cross-Coupling Reactions for Indoles , which covers palladium, copper, rhodium, iron, and nickel cross-couplings of indole - a suite of reactions that has assumed great importance in indole synthesis and chemistry. 

Darses and co-workers have published a series of papers on the synthesis of stereo-defined trisubstituted alkenes by the coupling of readily available unreactive MBH adducts with either organoboronic acids or potassium tri-fluoro(organo)borates in the presence of a rhodium complex via a reaction pathway involving a 1,4-addition/p-hydroxy elimination mechanism. Compared with the aforementioned Pd-catalyzed cross-coupling reaction, this reaction does not need the activation of the hydroxyl group with acetate or carbonate therefore it is more desirable, particularly in terms of atom economy. For the MBH adducts derived from methyl acrylates, the initial reported catalyst, [ Rh-(cod)Cl 2], was active at 50 °C for boronic acids and at 70 °C... 

A rhodium-catalyzed protocol of alkyne cyclooligomerization provides an alternative route for the preparation of indenocorannulenes 100 [27] (Scheme 29). The key step of the synthesis starts with 2,3-diethynylcoranulenes 99, which are accessed by Pd-catalyzed cross-coupling reactions of the corresponding 2,3-dichlorocorannulenes 19/23 with trimethyltin-substimted alkynes. The... 

The ready availability of arylboronates by an aromatic C-H borylation provides a synthetic link to the well-established palladium-catalyzed cross-coupling reactions, rhodium-catalyzed 1,4-addition to a,p-unsaturated carbonyl compounds, and other bond forming reactions using arylboronic esters (Scheme 2.12). Borylation of 1,3-dichlorobenzene with pinacolborane is followed directly by a cross-coupling reaction with methyl p-bromobenzoate for the synthesis of a biaryl product in 91% yield [60]. Pinacol esters of arylboronic acids react much slower than the free acids [62], but both derivatives achieve high isolated yields and comparable enantioselectivities (91% ee) in asymmetric 1,4-addition to N-benzyl crotonamides [63]. Borylation of arenes followed by oxidation of the C-B bond is synthetically equivalent to an aromatic C-H oxidation to phenols [64]. Oxidation of the resulting arylboronates with Oxone in a 1 1 acetone-water solution is completed within 10 min at room temperature. 

Despite being a less obvious starting material than a l,3-butadiene-2-yl coupling partner, l,2-butadien-4-yl precursors (such as 166 in Suzuki s pioneering example in Scheme 1.26) have seen the most use in dendralene synthesis [118, 131-136]. A couple of more recent examples include the palladium-catalyzed cross-coupling reaction of alkenyl bromides 179 with, for example, the organoindium derived from allenyl bromide 181, or 1,1-dimethyl allene (183) (via a Mizoroki-Heckreaction) (Scheme 1.28) [132,135]. Palladium(0)-catalyzed dimerizations or homocouplings can also furnish the C2-C3 bond [138-142], as can nickel(O)- [143,144] and rhodium(I)-catalyzed ones [137]. 

Carbon-carbon bond-forming reactions are one of the most basic, but important, transformations in organic chemistry. In addition to conventional organic reactions, the use of transition metal-catalyzed reactions to construct new carbon-carbon bonds has also been a topic of great interest. Such transformations to create chiral molecules enantioselectively is therefore very valuable. While various carbon-carbon bond-forming asymmetric catalyses have been described in the literature, this chapter focuses mainly on the asymmetric 1,4-addition reactions under copper or rhodium catalysis and on the asymmetric cross-coupling reactions catalyzed by nickel or palladium complexes. 

In a detailed investigation of the mechanism and scope of palladium catalyzed amination of five-membered heterocycles, the 1-methyl-3-bromoindole 145 was aminated with secondary amines to the 3-aminoindoles 146. Similar results were obtained for l-methyl-2-bromoindole <03JOC2861>. Rhodium-catalyzed cyclopropanation reactions involving 1-methyl-3-diazooxindole and exocyclic alkenes provided novel dispirocyclic cyclopropanes <03SL1599>. New applications of palladium-mediated cross-coupling reactions have been utilized to prepare a variety of functionalized indoles. Suzuki-Miyaura coupling reactions of indole-3-boronates <03H(59)473> and indole-5-boronates <03H(60)865> were utilized to prepare inhibitors of lipid peroxidation and melatonin analogues, respectively. 

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