Regioselective palladium-catalyzed

A parallel synthesis of a library of 2-aryl-6-chlorobenzothiazoles 112 involves a regioselective palladium-catalyzed Suzuki coupling reaction of 2,6-dichlorobenzothiazole 111 with arylboronic acids (1.1 equiv) under microwave irradiation <06TL3091>. When excess phenylboronic acid is used, Pd(PPh3)4 still provides 2-phenyl-6-chlorobenzothiazole exclusively, while 2-dicyclohexylphosphinobiphenyl 113 generates 2,6-diphenylbenzothiazole as the major product. 

Stereo- and regioselective palladium-catalyzed oxidation of 1,3-dienes in acetic acid to give l,4-diacetoxy-2-alkenes has been accomplished using Mn02 and catalytic amounts of p-benzoquinone (BQ)11. The reaction can be made to take place with cis- or trans-1,4-diacetoxylation across the diene in cyclic systems as shown in equation 6. 

Regioselective palladium-catalyzed arylation of ethyl 3-futoate at either the 2- or the 5-position can be achieved by the judicious choice of solvent and palladium catalyst, as shown in Scheme 27. However, efficient arylation requires the use of aryl bromides substituted with electron-withdrawing groups (e.g., NO2) <20030L301>. This method was applied to the synthesis of furo[3,2- ]quinolinone from l-bromo-2-nitrobenzene. 

An elegant application of regioselective palladium-catalyzed direct arylations of anilides in the presence of stoichiometric amounts of AgOAc in trifluoroacetic acid [65] permitted the preparation of chiral diamines with varying steric demands (Scheme 9.28) [66]. 

C—H bond arylations of electron-deficient heteroarenes, such as azines, remain highly challenging. An elegant and versatile solution was recently elaborated, however, through a redistribution of electron density in the starting pyridine by chemical modification [77, 78]. It was found that pyridine N-oxides smoothly underwent regioselectively palladium-catalyzed direct arylations with a variety of aryl bromides (Scheme 9.36) [77a]. 

A regioselective palladium-catalyzed hydrodebromination of 4,6-dibromoindoles produced the corresponding 4-bromoindoles <04JOC3336>. This chemistry was utilized in a key step in the preparation of the antihypertensive agent, U86192A 211. 

Andersson, C.M. and Hallberg, A. (1988) Regioselective palladium-catalyzed arylation of vinyl ethers with 4-nitrophenyl triflate. Control by addition of halide ions. J. Org. Chem., S3, 2112-4. 

Maes and co-workers developed a regioselective palladium-catalyzed synthesis of dipyrido[l,2-a 2, 3 -d]imidazole in 2006. Their methodology either... 

Figure 5.9 Diphosphine ligands for n-regioselective palladium-catalyzed hydroformylation.

Recently, de Lera et al. have carried out regioselective palladium-catalyzed crosscoupling reactions, Suzuki coupling and Stille coupling, in the synthesis of novel 2,3-disubstituted thiophene derivatives. They reported that regioselective coupling at C2 could be accomplished efficiently by Suzuki coupling under similar conditions (Equations 33 and 34) [34]. 

Two regioselective palladium-catalyzed methods have been developed for the direct C-H arylation of oxazole at C-5 or C-2 using aryl and heteroaryl bromides, chlorides, iodides, and tri-flates (eq SS). " Under optimized conditions, minor amounts (<10%) of the bis(arylated) product are observed. The reaction works well with arenes containing electron-donating or electron-withdrawing substituents. 

Methylenecycloalkanes have been found to undergo a regioselective, palladium-catalyzed hydrocarboxylation reaction with formic acid and carbon monoxide to give cycloalkylacetic acids in good yield. In the case of camphene, carbon monoxide pressures of 40 atm are required to achieve satisfactory conversions (eq 99). ... 

The reactions between benzotriafulvenes and transition metals (Pt and Rh) afford metallacyclobutane derivatives 41 as stable crystalline compounds in good yields. Recently, Huang developed the highly regioselective palladium-catalyzed [i+2] cycloaddition reactions of 34 (R = Ph) with arynes or alkynes to provide fluorene 42 and rndene derivatives 43, respectively (Scheme 6.4) [24]. 

S. Cacchi, G. Fabrizi, L. Moro, P. Pace, Stereo- and regioselective palladium-catalyzed hydroarylation and hydrovinylation of functionalised alkynes a route to substituted Z-2-cinnamyl esters, 3-chromen-2-ols, and coumarins, S)fnlett (1997) 1367-1370. 

Xiao W, VasapoUo G, Alper H. Highly regioselective palladium-catalyzed thiocarbonylation of allenes with thiols and carbon monoxide. J. Org. Chem. 1998 63 2609-2612. 

An efficient synthesis of the imidazo[l,2-b]pyrazole core has been developed and the first regioselective palladium catalyzed direct arylation of the C-3 position has been described by Grosse et al. (2012). Good to excellent yields were obtained for a extensive range of aryl partners with electron-rich and electron-poor substituents. This method allows rapid access to a large variety of imidazo[l,2-b] pyrazole products and could open the way to the design of new biologically active compounds. 

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