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Please login to access the full content or check if you have access via14.2.1.1.2.2 Method 2: Ring Closure of 3-Aryl-1-(2-hydroxyaryl)prop-2-en-1-ones (2′-Hydroxychalcones) to Flavylium Salts
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Nógrádi, M., Science of Synthesis, (2003) 14, 220.
2′-Hydroxychalcones are readily available by condensation of 2-hydroxyacetophenones and aryl aldehydes. Ring closure in the presence of triethyl orthoformate proceeds via a 2-aryl-2,3-dihydro-4H-benzopyran-4-one. It is accompanied by dehydrogenation and leads to 2-aryl-4-ethoxy-1-benzopyrylium salts 31 in 25–55% yield (Scheme 36),[137,138] while borohydride reduction followed by dehydration, acid treatment, and reoxidation with benzo-1,4-quinone gives 2-aryl-1-benzopyrylium salts unsubstituted at C4.[48,139]
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References
[48] | Meeeeeee, M., Meeeee Meeeeee Mee. Meee., (8888) 888, 888. |
[113] | Meeeeeeee, M.; Meeeeeeee, M.; Meeeeeeeee, M. M., Meee. Meeeeeeeeee. Meeeee., (8888), 888; Meee. Meeee., (8888) 88, 88888. |
[137] | Meeeeeeeeee, M. M.; Meeeeeeeee, M. M., Me. Mee. Meee., (8888) 8, 8888; Meee. Meeee., (8888) 88, 88888. |
[138] | Meeeeeeeeee, M. M.; Meeeeeeeee, M. M., Me. Mee. Meee., (8888) 8, 8888; Meee. Meeee., (8888) 88, 88888. |
[139] | Meeee-Meeee, M. M.; Meeeeee, M. M., Meee. M. Meee., (8888) 88, 8888. |
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- 8.Meeeee-Meee, (8888) M 8e, 88.