Rhodium-catalyzed arylations, heterocycles

Lewis JC, Wu JY, Bergman RG, EUman JA (2006) Microwave-promoted rhodium-catalyzed arylation of heterocycles through C-H bond activation. Angew Chem Int Ed 45 1589-1591... 

The synthesis of fused oxepines by transition metal-catalyzed reactions continues to be a major method for the formation of this heterocyclic system and can be separated into two types of transformations, those that react as tethered ethers and those that involve the reaction of an alcohol to form the seven-membered ring. The cyclization of tethered ethers included Heck cyclization (14EJO4053, 14CEJ17119), rhodium-catalyzed arylation of alkynes... 

The rhodium-catalyzed arylation of heterocycles was also proposed to proceed by an electrophihc aromatic pathway [83]. When using [RhCl(CO) P[OCH(CF3)2]3 2... 

In addition to palladium catalysts, Co(OAc)2 shows a catalytic activity for the arylation of heterocycles, including thiazole, oxazole, imidazole, benzothiazole, benzoxazole, and benzimidazole.78 As shown in Scheme 6, the catalytic system Co(OAc)2/9/Cs2C03 gives G5 phenylated thiazole, while the bimetallic system Co(OAc)2/CuI/9/Cs2C03 furnishes the G2 phenylated thiazole. The rhodium-catalyzed reaction of heterocycles such as benzimidazoles, benzoxazole, dihydroquinazoline, and oxazoline provides the arylation product with the aid of [RhCl(coe)]2/PCy3 catalyst.79 The intermediacy of an isolable A-heterocyle carbene complex is proposed. 

Rhodium-Catalyzed C-H/C-X Arylation of Arenes Through /V-Heterocyclic... 

Lewis JC, Wiedemann SH, Bergman RG, EUman JA (2004) Arylation of heterocycles via rhodium-catalyzed C-H bond functionalization. Org Lett 6 35-38... 

Intermolecular direct arylations of heteroarenes, such as indoles, pyrroles or (benzo)furans, were, thus far, predominantly achieved with palladium catalysts (see Chapter 10). However, rhodium complexes proved also competent for the direct functionaUzations of various valuable heteroarenes with comparable or, in some cases, improved catalytic performance. Thus, rhodium-catalyzed C—H bond functionalizations of various N-heterocycles, were elegantly developed by Bergman, Ellman and coworkers. Here, the use of a catalytic system comprising [RhCl(coe)2]2 and PCys led to direct arylations of unprotected benzimidazoles with aryl iodides... 

The Rh-BINAP-catalyzed intramolecular Alder-ene cycloisomerization is very rapid and, therefore, sequentially Rh-catalyzed sequences for the efficient enantioselective generation of five-membered carbo- and heterocycles were envisioned. Korber et al. [21] reported the enantioselective rhodium-catalyzed cycloisomerization of alkyl and (hetero)aryl alkynyl allyl alcohols for the generation of aldehyde-bearing chiral 4-alkyl 3-alkylidene THFs and tetrahydro-furanones, which were converted into a,P-unsaturated carbonyl side chains in a one-pot manner via a concluding Wittig olefination in good yields. 

As an alternative to addition of anionic nucleophiles followed by reoxidation, rhodium(l)-catalyzed C-H activation allowed the nucleophilic addition of alkenes to the intermediate Rh(i) carbene complex <2002JA13964, 2004JOC7329>. Purine behaved anomalously compared to other heterocycles, for which selective monoalkylation was observed, and underwent sequential substitution first at C-8 and then at C-6 (Equation 8). Caffeine was monoalkylated at C-8 in low yield (15%). Selectivity for C-8-arylation was also observed in the palladium-catalyzed C-H activation of 6-phenyl-9-benzylpurine (aryl iodides, 0.05 equiv Pd(OAc)2, 3 equiv Cul, 2.5 equiv CS2CO3, DMF, 160 °C, 60 h, 48-95% yields) <2006OL5389>. 

Ishiyama and Hartwig disclosed a set of rhodium(I)-catalyzed intermolecular Heck-type reactions between aryl iodides and N-heterocyclic aldimines to form the corresponding ketimines. Ishiyama T, Hartwig J (2000) 122 12043... 

Zhang L, Wu J (2008) Rhodium/N-heterocyclic carbene-catalyzed cross-couplings of aryl arenesulfonates with arylboronic acids. Adv Synth Catal 350 2409-2413 See also [124]... 

A new enantioselective Rh-catalyzed domino transformation of boronic acids with a cyclohexadienone-tethered alkyne gave access to fused heterocycles by desymmetrization of alkyne-tethered cyclohexadienones via the formation of two new C-C bonds and two new stereocenters with good enantioselectivities, syn-addition of the rhodium-aryl species onto the alkyne (130L1148). 

Alternatively, they were also found to be good racemization catalysts. Iridium complexes, but also rhodium compounds, catalyzed the racemization step in the enzymatic dynamic kinetic resolution of secondary alcohols, and excellent results were reported for alkyl-aryl as well as dialkyl secondary alcohols. Finally, picolyl and pyridine functionalized N-heterocyclic carbene iridium complexes [(C N)Ir(Cp )Cl]Cl were moderately active catalysts for the polymerization of norbomene in the presence of methylaluminoxane as cocatalyst. ... 

Almost simultaneously, Hua and co-workers developed a versatile and straightforward route to construct multisubstituted isoquinolines and relative fused pyridine heterocycles (60) by using readily availableketones (59) and alkynes (Scheme 7.41) [110]. The reaction involves condensation of aryl ketones and hydroxylamine, rhodium(III)-catalyzed C-H bond activation of the in situ generated aryl ketone oximes, and cycUzation with internal alkynes. This reaction proceeds under external-oxidant-free and moderately mild conditions. Later, a similar one-pot multi-component process promoted by a Rh(III) catalyst that generates substituted isoquinolines under microwave irradiation conditions was uncovered by Jun [111]. 

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