[reaction: see text] The value of arylboranes as precursors for arylzinc reagents in asymmetric catalysis is demonstrated. Kinetic studies on the transmetalation reaction with zinc reagents rationalize the observed differences of three classes of arylboranes in catalytic applications. By using the stable and easily accessible triarylborane ammonia complexes, an array of chiral diarylmethanols in high yield and enantioselectivity was synthesized.

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Diaryl ethers are important structures found in both nature and biologically active compounds. Some diaryl ethers exert considerable pharmacological activity, such as perrottetines, riccardin B, and marchantin quinone, all of which influence blood coagulation; 1 the antiviral cyclic peptide K-13; 2 and the glycopeptide antibiotics Vancomycin, Teicoplanin, and Complestatin. 2-5 Until recently, the synthesis of diaryl ethers having sensitive groups remained a challenge. 6-8 Therefore, diaryl ethers are a promising class of potentially useful pharmacologically active compounds, and their synthesis in liquid phase, particularly by nucleophilic aromatic substitution and Ullmann-type reactions, has found widespread application in organic chemistry. 9 The solid-phase synthesis of diaryl ethers mainly focuses on nucleophilic displacement of fluoronitroarenes in an intermolecular or intramolecular sense, furnishing 7-, 10 13-, 11 14-, 11-13 15-, 16-, 11,12,14 and 17-membered rings, 11 as demonstrated in the total synthesis of OF 4949. 14 Analogously, cyclic alkylaryl ethers 15 and thioethers 16 were synthesized using this strategy. Results and DiscussionWe were intrigued by the possibility of generating diaryl ethers on solid supports using the Ullmann reaction variant reported by Nicolaou et al., 5 since this reaction is particularly suitable for the synthesis of triazenyl-substituted diaryl ether and has been used in the total synthesis of the glycopeptide antibiotic Vancomycin. 5,17 The reaction temperature required is in contrast to classical Ullmann conditions compatible with solid-phase chemistry. Triazenes are masked diazonium ions and are convertible to a broad range of heterocycles. 18 In this manuscript, we disclose the first solid-phase UllmannNicolaou reaction.The required ortho-halo triazene resins 1{1-6} were synthesized via optimized procedures from anilines and arylmethylaminomethyl polystyrenes, which are available from chloromethylated polystyrene (1-2% cross-linked) in one synthetic step in large quantities (Scheme 1). 19,20 Five different anilines 21 were immobilized on benzylaminesubstituted Merrifield resin under standard conditions using this route. 22 The loadings were determined by elemental analysis.The Nicolaou variant of the Ullmann reaction was performed on the resins 3{1-4} (500-mg scale) at 75-85°C in acetonitrile/pyridine or dimethylformamide/pyridine for 36-48 h with 1.1-5.0 equiv of eight different phenols 4{1-8} 21 in the presence of the soluble copper complex CuBr‚SMe 2 (1 equiv) (Scheme 2). During the reaction, a color change of the resin from a slightly reddish color into a deep red color was observed. Heteroatoms such as nitrogen or oxygen atoms and simple functional groups (double bonds, amides, amines) at the phenolic moiety were tolerated; however, it was puzzling to note that extension to mono and

The effects of additives in phenylzinc addition reactions to an aldehyde have been studied using an automated high-throughput screening approach. With 2-bromobenzaldehyde as test substrate and N,N-dibutylnorephedrine (dbne) as chiral ligand, an improvement of 20% ee over the catalyzed reaction in the absence of the additive was observed. The described results enable a novel access towards chiral diarylmethanols using commercially available substrates, reagents and ligands as well as fast, automated techniques.

Synthesis of novel fluoronitroaryl triazenes in liquid phase and on solid support have been described; mild displacement of the fluoride ion with various nucleophiles provides access to substituted arenes which in turn can be cleaved to provide a unique access to 1-alkyl-5-nitro-1H-benzotriazole.