A new method for annulation of the α-pyrone ring

Abstract

New derivatives of coumarin, containing annulated α-pyrone rings, were obtained by reaction of the borate complexes of three isomeric acyl(hydroxy)coumarins with acid anhydrides. It was shown that the borate complex of 3-acetyl-4-hydroxy-2-pyrone also condenses with acetic anhydride to form a derivative containing a new annulated α-pyrone ring.

4-Hydroxy-3-[(2E)-3-(3,4,5-trimethoxyphenyl)prop-2-enoyl]-2H-chromen-2-one

“…For bond-length data, see: Traven et al(2000). For the exclusive annulation of the -pyrone ring, see Traven et al(2007). For charge transfer from the phenyl ring to the coumarin system, see Indira et al (2002); Sun & Cui (2008).…”

“…It was established that the condensation of the borate complexes of acyl(hydroxy)coumarins (Traven et al, 2007) with carboxylic acid anhydrides led to exclusive annulation of the α-pyrone ring. First, we prepare the borate complex of 4-hydroxycoumarin by the reaction of boron trifluoride etherate (1 g, 7.3 mmol) with the 3-acetyl-4-hydroxycoumarin (1.5 g, 7.3 mmol) in toluene (25 ml).…”

Substituted Quinolinones. Part 19. New and Unexpected Results from Oxidation of 3-Acetyl-1-Alkyl- 4-Hydroxyquinolin-2(1H)-Ones Using Selenium Dioxide

“…Since it is known that complex formation of acetyl derivatives with boron compounds substantially increases the reactivity of the methyl group of the acetyl moiety, 24,25 it was expected that boron complexes obtainable from the acetyl derivatives 1a, b are capable to undergo facile oxidation with selenium dioxide. In the same time, utilizing acetyl-boron chelate complexes may remove or avoid any effect of the hydroxyl group at position-4; like H-bonding or enhancement of enol-ketone tautomerism.…”

Synthesis of New Quinolinones from 3-Nitropyranoquinolinones

“…Complex formation of acetyl derivatives with boron compounds substantially increases the reactivity of the methyl or methylene group. 18,19 Therefore, additional support for the structures assigned to acids 4a,b and 5a,b was achieved through the conversion of 3-nitroacetyl derivatives 3a,b to nitroacetyl boron chelate complexes 7a,b which are capable of undergoing facile oxidation with selenium dioxide (Scheme 4). The 1 H NMR spectrum of 7a exhibited a characteristic singlet at δ 5.86.…”