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Synthesis of Benzofurans

Recent Literature

Substituted benzofurans were synthesized from their corresponding substituted 1-allyl-2-allyloxybenzenes using ruthenium-catalyzed C- and O-allyl isomerization followed by ring-closing metathesis.
W. A. L. van Otterlo, G. L. Morgans, L. G. Madeley, S. Kuzvidza, S. S. Moleele, N. Thornton, C. B. de Koning, Tetrahedron, 2005, 61, 7746-7755.

An effective and mild microwave-assisted route to 2-substituted benzofurans directly from carboxylic acids allows the preparation of α-alkyl-2-benzofuranmethanamines from N-protected α-amino acids without racemization in good yields.
L. De Luca, G. Giacomelli, G. Nieddu, J. Org. Chem., 2007, 72, 3955-3957.

TFAA induces a [3,3]-sigmatropic rearrangement of N-trifluoroacetyl-ene-hydroxylamines for the synthesis of dihydrobenzofurans, whereas reactions with TFAT-DMAP gives benzofurans. The synthetic utility is demonstrated by the short synthesis of natural benzofurans without protection of the hydroxy group.
N. Takeda, O. Miyata, T. Naito, Eur. J. Org. Chem., 2007, 1491-1509.

Copper-TMEDA catalyzes the transformation of readily available ketone derivatives into the corresponding benzo[b]furans in good to excellent yields. The sustainable protocol uses water as the solvent without organic cosolvents, and one example of catalyst reutilization is also presented.
M. Carril, R. SanMartin, I. Tellitu, E. Dominguez, Org. Lett., 2006, 8, 1467-1470.

An efficient CuI-catalyzed ring closure of 2-haloaromatic ketones gives a wide variety of benzo[b]furans.
C.-Y. Chen, P. G. Dormer, J. Org. Chem., 2005, 70, 6964-6967.

An efficient, indirect anti-Markovnikov hydration of unsymmetrically substituted terminal and internal alkynes is based on TiCl₄-catalyzed hydroamination reactions. Its application to ortho-alkynylhaloarenes, followed by a copper-catalyzed O-arylation, provides substituted benzo[b]furans.
L. Ackermann, L. T. Kaspar, J. Org. Chem., 2007, 72, 6149-6153.

Zn(OTf)₂ catalyzed the cyclization of propargyl alcohols with anilines and phenols in toluene at 100°C without additive and gave various indole and benzofuran products with different structures. The cyclization of propargyl alcohols and amides gave oxazoles. Mechanisms for the different substituation patterns are discussed.
M. P. Kumar, R.-S. Liu, J. Org. Chem., 2006, 71, 4951-4955.

A convenient high-yielding, efficient, selective and simple one-pot procedure for the synthesis of 3-ethoxycarbonylbenzofurans from commercially available salicylaldehydes and ethyl diazoacetate has been developed.
M. E. Dudley, M. M. Morshed, M. M. Hossain, Synthesis, 2006, 1711-1714.

CuI-catalyzed coupling of 1-bromo-2-iodobenzenes with β-keto esters in THF at 100°C provides 2,3-disubstituted benzofurans. This domino transformation involves an intermolecular C-C bond formation and a subsequent intramolecular C-O bond formation process.
B. Lu, B. Wang, Y. Zhang, D. Ma, J. Org. Chem., 2007, 72, 5337-5341.

The Pt-catalyzed cyclization of o-alkynylphenyl acetals produces 3-(-alkoxyalkyl)benzofurans in good to high yields. The mechanism is discussed.
I. Nakamura, Y. Mizushima, Y. Yamamoto, J. Am. Chem. Soc., 2005, 127, 15022-15023.

A one-pot method for the preparation of alkyl aryl ethers from aryl halides and the preparation of substituted benzofurans via a Pd-catalyzed phenol formation/cyclization protocol starting from 2-chloroaryl alkynes are described.
K. W. Anderson, T. Ikawa, R. E. Tundel, S. L. Buchwald, J. Am. Chem. Soc., 2006, 128, 10694-10695.

2,3-Disubstituted benzo[b]furans are readily prepared under very mild reaction conditions by the Sonogashira coupling of various o-iodoanisoles and terminal alkynes, followed by an electrophilic cyclization. Aryl- and vinylic-substituted alkynes give cyclization products in excellent yields.
D. Yue, T. Yao, R. C. Larock, J. Org. Chem., 2005, 70, 10292-10296.