Categories: Synthesis of O-Heterocycles > benzo-fused O-Heterocycles >
Synthesis of 2H-chromenes (2H-benzopyrans)
Recent Literature
A mild, electrophilic cyclization of substituted propargylic aryl ethers by I2,
ICl, and PhSeBr produces 3,4-disubstituted 2H-benzopyrans in excellent
yields. This methodology tolerates various functional groups, such as methoxy,
alcohol, aldehyde, and nitro groups.
S. A. Worlikar, T. Kesharwani, T. Yao, R. C. Larock, J. Org. Chem., 2007,
72, 1347-1353.
Under base-free conditions, readily accessible 2-ethoxy-2H-chromenes
undergo C-O activation and C-C bond formation in the presence of an inexpensive
nickel catalyst and boronic acids. This modular and highly efficient protocol
enables broad access to 2-substituted-2H-chromenes and has been applied
to the late-stage incorporation of complex molecules.
T. J. A. Graham, A. G. Doyle, Org. Lett., 2012,
14, 1616-1619.
A transition-metal-free coupling of various triorganoindium reagents with
chromene and isochroman acetals in the presence of BF3ˇOEt2
afforded 2-substituted chromenes and 1-substituted isochromans, respectively, in
good yields. The reactions proceed with only 50 mol % of the organometallic,
thus demonstrating the efficiency of these species.
J. M. Gil-Negrete, J. P. Sestelo, L. A. Sarandeses, Org. Lett.,
2016, 18, 4316-4319.
The Petasis condensation of vinylic or aromatic boronic acids,
salicylaldehydes, and amines is assisted by the hydroxy group adjacent to the
aldehyde moiety. A subsequent cyclization with ejection of amine upon heating
provides 2H-chromenes. A catalytic method using a resin-bound amine
enables a convenient preparation of 2H-chromenes.
Q. Wang, M. G. Finn,
Org. Lett., 2000, 2, 4063-4065.
The annulative condensation of salicylaldehydes and acrylonitrile to give
3-cyano-2H-chromenes is efficiently mediated by 4-dimethylaminopyridine (DMAP).
The reaction yielded 3-cyano-2H-chromenes in higher yields with DMAP than
with DABCO in most cases and remains high yielding even in decagram-scale.
B. Kang, K. Ikeda, Chem. Pharm. Bull., 2023, 71, 318-325.
A solvent-controlled and rhodium(III)-catalyzed C-H activation/[3 + 3]
annulation sequence enables an efficient and redox-neutral synthesis of 2H-chromene-3-carboxylic acids
from N-phenoxyacetamides and methyleneoxetanones as a three-carbon source.
Z. Zhou, M. Bian, L. Zhao, H. Gao, J. Huang, X. Liu, Y. Yu, X. Li, W. Yi, Org. Lett.,
2018, 20, 3892-3896.
Diarylprolinol silyl ether catalyzes an asymmetric enantioselective domino
oxa-Michael-Mannich-[1,3]-amino rearrangement reaction of N-tosylsalicylimines
with a wide range of α,β-unsaturated aldehydes to produce the corresponding
chair N-tosylimines-chromenes with excellent enantioselectivity and yield. The
reaction tolerates a range of functional groups.
S. Hu, J. Wang, G. Huang, K. Zhu, F. Chen, J. Org. Chem., 2020, 85,
4011-4018.
A structurally simple and easily accessible l-proline derived aminocatalyst
provides 2-alkyl/aryl-3-nitro-2H-chromenes in excellent
enantioselectivity within a short reaction time via an asymmetric tandem
oxa-Michael-Henry reaction of salicylaldehyde with conjugated nitroalkene.
R. Mohanta, G. Bez, J. Org. Chem., 2020, 85,
4627-4636.
A cascade oxa-Michael-Henry reaction of salicylaldehyde derivatives with
β-nitrostyrenes is catalyzed by potassium carbonate using solvent-free ball
milling to provide 3-nitro-2H-chromenes in good yields. This method
offers short reaction times and mild conditions.
S.-X. Liu, C.-M. Jia, B.-Y. Yao, X.-L. Chen, Q. Zhang,
Synthesis, 2016, 48, 407-412.