Synthesis of benzo-fused O-Heterocycles and similar compounds
A nucleophilic substitution of alkyl fluorides was achieved in intramolecular reactions with O- and N-nucleophiles. The reaction is influenced by the nature of nucleophiles, the size of the ring to be formed, and the comformational rigidity of the precursors.
L. Zhang, W. Zhang, J. Liu, J. Hu, J. Org. Chem., 2009, 74, 2850-2853.
A broad range of substituted benzisoxazolines have been synthesized by a mild [3 + 2] cycloaddition of nitrones and arynes. The process tolerates various functional groups.
C. Lu, A. V. Dubrovskiy, R. C. Larock, J. Org. Chem., 2012, 77, 2279-2284.
Iron(II) bromide catalyzes the transformation of aryl and vinyl azides with ketone or methyl oxime substituents into 2,1-benzisoxazoles, indazoles, or pyrazoles through the formation of an N-O or N-N bond. This transformation tolerates various functional groups and facilitates access to a range of benzisoxazoles or indazoles.
B. J. Stokes, C. V. Vogel, L. K. Urnezis, M. Pan, T. G. Driver, Org. Lett., 2010, 12, 2884-2887.
Sequential coupling-imination-annulation reactions of ortho-bromoarylaldehydes and terminal alkynes with ammonium acetate in the presence of a palladium catalyst under microwave irradiation gives various substituted isoquinolines, furopyridines, and thienopyridines in good yields.
D. Yang, S. Burugupalli, D. Daniel, Y. Chen, J. Org. Chem., 2012, 77, 4466-4472.
An effient tandem process consisting of palladium-catalyzed double-bond isomerization of long-chain olefins followed by intramolecular cyclization promoted by B2(OH)2 provides benzo-fused oxazaheterocycles. This strategy also provides rapid access to pyrido[3,4-b]indoles, trans-2-olefins, and enamides with high regio- and stereoselectivity.
L. Ding, Y.-N. Niu, X.-F. Xia, J. Org. Chem., 2021, 86, 10032-10042.
Phenols react with nitriles and dimethyl sulfoxide (DMSO) in the presence of a catalytic amount of (COCl)2 in CH3CN or chloroform to afford the corresponding N-acylbenzoxazines in good yields. DMSO acts as a source of HCHO, which is generated in situ.
H. Wang, Z. Xi, S. Huang, R. Ding, Y. Gao, Y. Liu, B. Sun, H. Tian, S. Liang, J. Org. Chem., 2021, 86, 4932-4943.
A regioselective one-pot synthesis of 2-alkyl-3,4-dihydro-3-oxo-2H-1,4-benzoxazines under microwave heating starts from commercially available 2-aminophenols. Base-mediated regioselective O-alkylation with 2-bromoalkanoates gives acyclic intermediates. A subsequent intramolecular amidation reaction furnishes the desired products in good yields.
W.-M. Dai, X. Wang, C. Ma, Tetrahedron, 2005, 61, 6879-6885.
An Inverse Electron Demand Azo-Diels-Alder Reaction of o-Quinone Methides and Imino Ethers: Synthesis of Benzocondensed 1,3-Oxazines
D. V. Osipov, V. A. Osyanin, G. D. Khaysanova, E. R. Masterova, P. E. Krasnikov, Y. N. Klimochkin, J. Org. Chem., 2018, 83, 4775-4785.
A highly atom-efficient PIDA-mediated intramolecular iminoenol tautomer trapping reaction, followed by Et3N-promoted aerobic oxidative ring construction enables the synthesis of multisubstituted 2-hydroxy-benzo[b][1,4]oxazins from N-(2-hydroxylaryl)enaminones at room temperature under air. O2 serves as the oxygen source of the hydroxyl group.
H. Zhang, J. Shen, G. Cheng, Y. Feng, X. Cui, Org. Lett., 2018, 20, 664-667.
A base-catalyzed intramolecular defluorination/O-arylation of readily available α-fluoro-β-one-sulfones provides a series of 3-fluoro-1,4-oxathiine 4,4-dioxide derivatives in very good yields. This process is triggered by a catalytic amount of tetramethylguanidine (TMG) as base and molecular sieves as both an adsorbent to remove HF acid and an activator to assist C-F bond cleavage.
L. Kang, J. Zhang, H. Yang, J. Qian, G. Jiang, Synlett, 2021, 32, 785-789.
N-heterocyclic carbene/copper-cocatalyzed [4 + 3] annulations of salicylaldehydes with aziridines provide the corresponding 1,4-benzoxazepinones in good yields with exclusive regioselectivity.
Y.-F. Han, Z.-H. Gao, C.-L. Zhang, S. Ye, Org. Lett., 2020, 22, 8396-8400.
An atom-economic, efficient, rapid, and highly regioselective one-pot click reaction allows the synthesis of benzo[e][1,4]oxazepin-5-ones in excellent yields. The method involves epoxide ring-opening-ring-closing cascade with anthranilic acids using neat grinding at room temperature in the presence of lithium bromide as a mild catalyst. Pure products are obtained simply by washing the reaction mixture with warm water.
A. K. Singh, R. Chawla, L. D. S. Yadav, Synthesis, 2012, 44, 2353-2358.
Dehydration of 1,6-diols by treatment with BF3ˇOEt2 in dichloromethane gave tetrahydrobenzoxepines in very good yields, whereas 1,7-diols did not undergo dehydration.
M. Yus, T. Soler, F. Foubelo, Tetrahedron, 2002, 58, 7009-7016.
Benzo-fused sulfamate-derived imines readily react with glycine aldimino esters in the presence of an amine base to furnish 1,3-benzoxazepine frameworks in good yields.
M. K. Reddy, V. Bhajammanavar, M. Baidya, Org. Lett., 2021, 23, 3868-3872.
A chiral phosphoric acid catalyst catalyzes an intramolecular reaction of a range of benzylic alcohols bearing an internal oxetane to form chiral 1,4-benzodioxepines with high enantioselectivity. This oxetane desymmetrization process enables a direct synthesis of seven-membered heterocycles with good stereocontrol.
X. Zou, G. Sun, H. Huang, J. Wang, W. Yang, J. Sun, Org. Lett., 2020, 22, 249-252.
A visible-light photocatalytic aerobic oxidative lactonization of arene C(sp2)-H bonds provides benzocoumarin derivatives in good yields in the presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and tert-butyl nitrite. This atom economic method offers mild reaction conditions, use of a green oxidant and metal-free catalysis.
Y. Wang, S. Wang, B. Chen, M. Li, X. Hu, B. Hu, L. Jin, N. Sun, Z. Shen, Synlett, 2020, 31, 261-266.
Iron photocatalysis enables a mild and efficient intramolecular aromatic C-H oxygenation of 2-biphenylcarboxylic acids to furnish benzocoumarins with a diverse array of substituents in very good yields.
S. Xia, K. Hu, C. Lei, J. Jin, Org. Lett., 2020, 22, 1385-1389.
A direct Pd-catalyzed arylation reaction for the intramolecular formation of biaryl compounds using a novel phosphine ligand offers enhanced catalytic activity for transformations of previously unreactive substrates.
L.-C. Campeau, M. Parisien, M. Leblanc, K. Fagnou, J. Am. Chem. Soc., 2004, 126, 9186-9187.