Related Products of 108-37-2, A common heterocyclic compound, 108-37-2, name is 1-Bromo-3-chlorobenzene, molecular formula is C6H4BrCl, its traditional synthetic route has been very mature, but the traditional synthetic route has various shortcomings, such as complicated route, low yield, poor purity, etc, below Introduce a new synthetic route.
This example illustrates the tandem Ir-catalyzed borylation and catalytic amination process. [0064] 3-Aminoboronic acids and esters as shown below are of interest as evidenced by the large number of derivatives synthesized, and by several patents, which note their activity as O-lactamase inhibitors (See, for example, Shoichet et al., WO0035905). Few in number, however, are 1, 3, 5-aminoboronic acids and esters (about 25 compounds by SCIFINDER SCHOLAR). Such substrates may prove useful for further derivatization as they can possess three unique sites for diversity. Furthermore, these compounds may prove ideal as scaffolds for combinatorial libraries. The boronic acid or ester can be transformed into a myriad of functionalities including aryl or vinyl via the Suzuki-Miyuara coupling (Miyaura and Suzuki, Chem. Rev. 95: 2457-2483 (1995); Suzuki, J. Organomet. Chem. 576: 147-168 (1999); Miyaura, In Advances in Metal-Organic Chemistry: Liebeskind, Ed.: JAI: London,; Vol. 6, pp. 187-243 (1998)). If R is a halogen, then there exists a multitude of coupling opportunities (See, for examples, Metal-catalyzed Cross-coupling Reactions; Diederich and Stang, eds.: Wiley: Wienheim, 1998). [0066] Recently, a catalytic aromatic C-H activation/borylation reaction utilizing Ir- or Rh-catalysts was developed. The process is high yielding, functional group tolerant (alkyl, halo, carboxy, alkoxy, and protected amino), chemoselective (1,3-substited arenes give only the 5-boryl product), and efficient (Iverson and Smith, J. Am. Chem. Soc. 121: 7696-7697 (1999); Cho et al., J. Am. Chem. Soc. 122: 12868-12869 (2000); Tse et al., Org. Lett. 3: 2831 (2001); Chao et al., Science 295: 305-308 (2002)). Furthermore, the process allows for the direct construction of aryl boronic esters from hydrocarbon feedstocks without going through an aryl halide. Scheme 2 depicts a prototypical borylation reaction: borylation of benzene using (Ind)Ir(COD)(2 mol %), dppe (2 mol %). The borane of choice is pinacolborane (HBPin). A variety of Ir(I) catalysts can be used, including [Ir(COD)Cl]2, Ir(Indenyl)(C2H4)2, Ir(Indenyl)dppe, and (Indenyl)Ir(COD), in the presence of 2 mol equivalents of PMe3 or 1 mol equivalent of a bidentate ligand like dmpe or dppe. The catalyst system of choice is (Indenyl)Ir(COD), dppe or dmpe (2 mol % each) because of it’s cleanness of reaction and efficient TOF (24 h-1 with benzene). The reaction can be run in the neat arene or in inert solvents (e.g. cyclohexane). During our studies into tandem borylation/Suzuki coupling, we noted difficulties with the hydrolysis of the boronic ester functionality (Bpin). The robustness of the BPin group suggested that, perhaps, the pinacol might serve as a protecting group for the boron. Thus, it was deemed of interest to explore other catalytic transformations in the presence of the BPin group. One such transformation is the Buchwald-Hartwig amination of aryl halides (See, for example; Wolfe et al.,. J. Org. Chem. 65: 1158 (2000); Hartwig et al., J. Org. Chem. 64: 5575 (1999); Wolfe and Buchwald, Angew. Chem. Int. Ed. 38: 2413 (1999)). Initially, the reaction was attempted on pure 1-chloro-3-methylphenyl-5-BPin. As shown in Scheme 3 (Buchwald-Hartwig coupling of 1-chloro-3-methylphenyl-5-BPin with aniline), application of Buchwalds protocol proceeded cleanly to give the desired cross-coupling product in 64.7% and 63.8% yield. The use of PtBu3 improved the yield to 78.8%. Unfortunately, initial attempts to perform the reaction in the ?one-pot? protocol were unsuccessful. Table 1 summarizes the results. In all cases where K3PO4.nH2O was used, a significant amount of pinacol was observed by GC-FID (Entries 1-5). While this is indicative of reaction of the BPin group and is most likely a by-product of Suzuki coupling (in this case, dimerization or oligiomerization of the starting material), no dimers or oligiomers were isolated. Noteworthy, is the formation of the desired product, albeit in low yield (10% GC-FID ratio), using K3PO4.nH2O and PtBu3 when all other attempts using the base failed. With anhydrous K3PO4, results were better (Entries 6-9). Most importantly, no pinacol was formed in these reactions. Changing the base or increasing catalyst loading did not improve the results. The use of PtBu3 led to the best results and after 4 days at 100 C., 34.4% of the desired product was isolated (Entry 10). This result, however, falls short of the reaction performed on pure material and shows that the by-products from the Ir-catalyzed borylation are not completely innocuous. As was previously mentioned, a potential source of concern is the presence of free bidentate phosphines after the borylation, which may interfere with subsequent reactions. In the tandem Suzuki reactions, an aryl chloride was successfully coupled only when dmpe was used as the Ir ligand. Thus, the tandem borylation/Buchwald-Hartwig amination reaction of the present invention was attempted using the (Ind)Ir(COD)/dmpe precatalyst….
The basis of chemical reaction formula synthesis, the synthesis route is composed of some specific reactions and combined according to certain logical thinking. We look forward to the emergence of more reaction modes in the future.
Reference:
Patent; Board of Trustees of Michigan State University; US2004/24237; (2004); A1;,
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