Reactions of 4-Oxo-4H-1-benzopyran-3-carboxaldehydes with Pentane-2,4-dione in Acidic Medium—a New Route to Dihydroxybenzophenone Derivatives

Abstract

Reaction of the title aldehyde 1 with acetylacetone 2 gives benzophenone 8 along with the Knoevenagel-type product 5 under acidic conditions.

Reactions of 3-Formylchromone with Active Methylene and Methyl Compounds and Some Subsequent Reactions of the Resulting Condensation Products

“…Product 7 was also synthesized in 60% yield by condensation of 1 and 2,4-pentanedione in acetic anhydride – sodium acetate medium [ 16 ]. Benzophenones 14 were obtained in low yields (15–30 %) along with 7 (30–40 %) by the addition of a solution of 1 in acetic acid to a preheated (70–80 ºC) mixture of 2,4-pentanedione in acetic acid containing a catalytic amount of hydrochloric acid [ 17 ]. The formation of 14 ( Scheme 2 , path c) can be explained by a mechanism which involves the acid-catalysed 1,4-addition of the enol form of 2,4-pentanedione to 1 , followed by ring opening to generate intermediate 10 , which then enolises to 12 .…”

“…When the mixture of 1 , 2,4-pentanedione and the catalytic amount of hydrochloric acid is treated in acetic acid at room temperature and then heated at 70–80ºC for 2 hrs, only products 7a and 7b , respectively, were isolated in 40–45% yields [ 17 ], which demosntrates 1,2 – addition of 2,4-pentane-dione to protonated 1 . On the other hand, the mechanism of base-catalysed condensation of 1 consists on the initial attack of the nucleophile at the C-2 of pyrone ring, followed by ring opening and recyclisation to 11 with subsequent elimination of water to give 7 ( Scheme 2 , path b) [ 2 , 16 ].…”