Coordinative role of alkali cations in organic synthesis. 2. The chalcone-flavanone system

Competition between Cyclization and Dehalogenation in the Photochemistry of Cinnamylphenols with Halogen Substituents at the Phenolic and Styrenic Chromophores

“…Preparation of the Substrates 1d,e. The cinnamylphenols 1d,e were prepared by reduction of the corresponding trans-2hydroxychalcones (previously synthesized by condensation of 2-hydroxyacetophenone with 4-chloro or 4-bromobenzaldehyde) 19 with LiAlH4/AlCl3, using tetrahydrofuran as solvent. 20 3032, 1485, 1409, 1308, 1205, 1160, 11051 H NMR 7.19-7.36 (m, 7H), 6.67 (d, 1H) 209 (100), 199 (22), 197 (23), 131 (19), 118 (29), 115 (23), 104 (48), 91 (19), 77 (18).…”

Coordinative role of alkali cations in organic synthesis. 3. Selective methylations of 5-hydroxy-2-hydroxymethyl-.gamma.-pyrone

“…No effort was made to make the conditions drastic to promote methylation of the alcoholic group for this cannot be done without simultaneous methylation of the phenolic OH.13 (iii) Synthesis of 4 by taking 1 (1.77 g), DMS (4.72 g), and NaOH (1.0 g) and employing a 132 (NaOH), 20 aq, DMS ((), 40-45 °C reaction. After addition of DMS was complete and the reaction solution had been allowed to rest for another 30 min, the pH was adjusted at 7 using 1 N NaOH.…”

“…Methylation of kojic acid (1) with dimethyl sulfate (DMS) in aqueous caustic alkalis (MOH) leads2™4 to all three possible ethers 2, 3, and 4. However, selective preparation of 3 and 4 in high yields was never achieved and it is not convenient to separate them.…”

A review of the syntheses of flavanones, thioflavanones, and azaflavanones from 2'‐substituted chalcones

“…Treatment of 2 0 -hydroxychalcone with LiOH in aq EtOH afforded the lithium chalconate intermediate (G), which underwent 1,4-addition to give flavanone (1) (Scheme 8). 23 Li + -π interaction enhanced the cationic character at the β carbon and facilitated the 1,4-addition of G.…”

“…2'-Hydroxychalcones were cyclized by reflux in a solution of sodium acetate in EtOH 28 or CH 3 OH 29 to give flavanones. For example, the reaction between prenylated 2'hydroxychalcones (23) and 10 equiv of NaOAc in EtOH at reflux afforded prenylated flavanones (24) (Scheme 10). Under these conditions, the protecting MOM group was retained.…”