Synthesis of Isocoumarins
An efficient and robust palladium-catalyzed nucleophilic addition/oxidative annulation of bromoalkynes with benzoic acids provides 3-substituted isocoumarins.
G. Jiang, J. Li, C. Zhu, W. Wu, H. Jiang, Org. Lett., 2017, 19, 4440-4443.
A BF3·Et2O-mediated 6-endo-dig cyclization process enables a general and efficient lactonization of readily available 2-alkynylbenzoates to provide biologically important isochromenones under mild conditions. An alternative mechanistic pathway in which BF3·Et2O activates the carbonyl of the ester moiety, rather than the alkyne triple bond, is postulated.
X. Zhang, X. Wan, Y. Cong, X. Zhen, Q. Li, D. Zhang-Negrerie, Y. Du, K. Zhao, J. Org. Chem., 2019, 84, 10402-10411.
A copper-catalyzed tandem C-C/C-O coupling strategy from readily available 2-iodo-N-phenyl benzamides and acyclic diketones as starting materials enables a facile and rapid synthesis of isocoumarin derivatives.
V. Kavala, C.-C. Wang, D. K. Barange, C.-W. Kuo, P.-M. Lei, C.-F. Yao, J. Org. Chem., 2012, 77, 5022-5029.
An efficient strategy for the synthesis of a variety of 3-substituted isocoumarins in very good yields proceeds from o-halobenzoic acids and 1,3-diketones via a copper(I)-catalyzed domino reaction in DMF under the action of K3PO4 at 90-120°C without a ligand.
S. Cai, F. Wang, C. Xi, J. Org. Chem., 2012, 77, 2331-2336.
A palladium-catalyzed α-arylation step followed by an intramolecular cyclization process enables the preparation of various isocoumarins directly from 2-halobenzoates and ketones. In case of 2-bromobenzoates, the addition of iodide anions to the reaction mixture increased yields and selectivities. This phosphine-free one-pot synthesis features a high functional group tolerance and gives access to richly decorated isocoumarins.
A. Casnati, R. Maggi, G. Maestri, N. Della Ca', E. Motti, J. Org. Chem., 2017, 82, 8296-8303.
A highly efficient palladium(0)-catalyzed strategy for the synthesis of isocoumarins involves cyclization with incorporation of tert-butyl isocyanide followed by simple acid hydrolysis to provide valuable lactones in good yields. The methodology is tolerant of a wide range of substrates and applicable to library synthesis.
X.-D. Fei, Z.-Y. Ge, T. Tang, Y.-M. Zhu, S.-J. Ji, J. Org. Chem., 2012, 77, 10321-10328.
A simple and highly efficient strategy for the synthesis of 3-substituted isocoumarins from 1-(2-halophenyl)-1,3-diones is based on a cascade copper(I)-catalyzed intramolecular Ullmann-type C-arylation and rearrangement process. This methodology tolerates a wide range of substrates and is applicable to library synthesis.
Z.-Y. Ge, X.-D. Fei, T. Tang, Y.-M. Zhu, J.-K. Shen, J. Org. Chem., 2012, 77, 5736-5743.
p-Toluenesulfonic acid (PTSA) in ethanol was used as a mild acid catalyst for the annulation of various functionalized diarylalkynes under microwave irradiation. This metal-free process allowed the synthesis of various 3-aryl-substituted isocoumarins in good yields.
G. Le Bras, A. Hamze, S. Messaoudi, O. Provot, P.-B. Le Calvez, J.-D. Brion, M. Alami, Synthesis, 2008, 1607-1611.
Addition of a catalytic amount of Cy2NH·HX improves the rate and yields for cyclization reactions of o-(alkynyl)benzoates in the presence of a stoichiometric amount of copper(II)halide to give 4-haloisocoumarins. Under the standard reaction conditions, various 4-haloisocoumarins are provided in good yield.
Y. Liang, Y.-X. Xie, J.-H. Li, Synthesis, 2007, 400-406.
A simple addition of o-halobenzoic acids to active internal alkynes proceeds efficiently in the presence of CuCl2 as a catalyst to give the corresponding isocoumarin derivatives.
X.-X. Guo, J. Org. Chem., 2013, 78, 1660-1664.