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Synthesis of Chromanones and Flavanones

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A cationic Ru-H complex is a highly effective catalyst for a mild deaminative coupling reaction of 2'-hydroxyaryl ketones with simple amines to form 3-substituted flavanone products. The analogous deaminative coupling reaction of 2-aminobenzamides with branched amines directly formed 3,3-disubstituted quinazolinone products.
K. Gnyawali, P. T. K. Arachchige, C. S. Yi, Org. Lett., 2022, 24, 218-222.

A facile ethylenediamine diacetate (EDDA)-catalyzed one-pot reaction of 2-hydroxyacetophenones, aromatic aldehydes, and aniline provides a rapid access to biologically interesting flavanone derivatives via a Mannich-type reaction. To demonstrate this method, several biologically interesting natural products bearing a flavanone moiety were synthesized.
S. V. N. Vuppalapati, L. Xia, N. Edayadulla, Y. R. Lee, Synthesis, 2014, 46, 465-474.

A N-heterocycle carbene (NHC)-catalyzed dual Stetter cascade reaction enables a coupling of β-nitrostyrene with phthalaldehyde under mild conditions to furnish valuable aryl-naphthoquinones, whereas the reaction of salicylaldehydes with β-nitrostyrene provides functionalized dihydroisoflavanones.
R. N. Mitra, K. Show, D. Barman, S. Sarkar, D. K. Maiti, J. Org. Chem., 2019, 84, 42-52.

DBU catalyzes a sequence of 1,4-conjugate addition of water to alkynyl o-quinone methide (o-AQM), followed by an alkyne-allene isomerization and subsequent intramolecular oxa-Michael addition to provide a broad range of flavanones in very good yields with good functional-group tolerance.
X. He, M. Xie, R. Li, P. Y. Choy, Q. Tang, Y. Shang, F. Y. Kwong, Org. Lett., 2020, 22, 4306-4310.

A broad range of flavanones were synthesized in very good yields via a palladium-catalyzed dehydrogenation of chromanones followed by arylation with arylboronic acids. This reaction provides a route to interesting natural products such as naringenin trimethyl ether.
H.-S. Yoo, S.-H. Son, Y. Y. Cho, S. J. Lee, H. J. Jang, Y. M. Kim, D. H. Kim, N. Y. Kim, B. Y. Park, Y. S. Lee, N.-J. Kim, J. Org. Chem., 2019, 84, 10012-10023.

An N-Heterocyclic carbene efficiently catalyzed an intramolecular nucleophilic substitution reaction to yield benzopyrones and benzofuranones depending on the substitution pattern.
J. He, J. Zheng, J. Liu, X. She, X. Pan, Org. Lett., 2006, 8, 4637-4640.

A borane catalyst generated in situ by hydroboration of pentafluorostyrene with HB(C6F5)2 enables a Piers-type hydrosilylation of chromones and flavones to afford a variety of chromanones and flavanones in very good yields.
X. Ren, C. Han, X. Feng, H. Du, Synlett, 2017, 28, 2421-2424.

Visible-light mediates a dual acylation of alkenes for the construction of 3-substituted chroman-4-ones in good yields via a radical tandem cyclization reaction. The reaction involves a carbon-carbon bond cleavage of oxime esters by a nitrogen-centered radical strategy.
Y.-C. Liu, P. Chen, X.-J. Li, B.-Q. Xiong, K.-W. Tang, P.-F. Huang, J. Org. Chem., 2022, 87, 4263-4272.

Chiral triazolium salts based on the camphor scaffold are highly efficient catalysts for the asymmetric intramolecular Stetter reaction. With a catalyst loading of 10 mol%, the desired products were obtained in excellent yields with up to 97% ee.
Z.-Q. Rong, Y. Li, G.-Q. Yang, S.-L. You, Synlett, 2011, 1033-1037.

The first enantioselective intramolecular catalytic Stetter reaction, which opens up a short and efficient pathway to enantiomerically enriched chroman-4-ones, is reported.
D. Enders, K. Breuer, J. Runsink, Helv. Chim. Acta, 1996, 79, 1899-1902.

A highly enantio- and diastereoselective intramolecular Stetter reaction has been developed. Aliphatic and aromatic aldehydes and a broad range of trisubstituted Michael acceptors have been found to afford the desired products in good overall yield with high enantio- and diastereoselectivity.
J. Read de Alaniz, T. Rovis, J. Am. Chem. Soc., 2005, 127, 6284-6289.