Zwitterionic and free forms of arylmethyl Meldrum's acids

Abstract

C-Alkyl (including C-arylmethyl) derivatives of Meldrum's acids are attractive building blocks in organic synthesis, mainly due to the unusually high acidity of the resulting compounds. Three examples, namely 5-[4-(diethylamino)benzyl]-2,2-dimethyl-1,3-dioxane-4,6-dione, C17H23NO4, (I), 2,2-dimethyl-5-(2,4,6-trimethoxybenzyl)-1,3-dioxane-4,6-dione, C16H20O7, (II), and 5-(4-hydroxy-3,5-dimethoxybenzyl)-2,2-dimethyl-1,3-dioxane-4,6-dione, C15H18O7, (III), have been synthesized, characterized by NMR and IR spectroscopy, and studied by single-crystal X-ray structure analysis. The nature of the different substituents resulted in remarkable differences in both the molecular conformations and the crystal packing arrangements. The presence of a substituent with a basic centre in compound (I) leads to the formation of an inner salt accompanied by drastic changes in the conformation of the 1,3-dioxane-4,6-dione fragment. By virtue of strong N-H···O hydrogen bonds, the residues are assembled into infinite chains with the graph-set descriptor C(10). Compound (II) contains methoxy groups in both the ortho- and para-positions of the arylmethyl fragment. Because of the absence of classical hydrogen-bond donors in this structure, the crystal packing is controlled by van der Waals forces and weak C-H···O interactions. Compound (III) contains methoxy groups in both meta-positions and a hydroxy group in the para-position. Supramolecular tetrameric synthons which comprise hydrogen-bonded dimers associated into tetramers through π-π interactions of overlapping benzene rings were observed.

Novel type of carbon‐centered antioxidants arylmethyl Meldrum's acids − inhibit free radicals

“…The obtained white solid (564 mg) was crystalized from ethanol (25 mL) leading to white crystals of target compound (320 mg, 55%) with Mp 143-144°C. The Mp and spectral data correspond to those given in literature [41].…”

“…The obtained solid (1.02 g) was crystalized from ethanol (80-90 mL) leading to the product as bright yellow crystals (0.8 g, 78%). The spectral data of the compound correspond to those given in literature [41]. Concentration of the antioxidant which inhibits 50% of the free radical (concentration of the solution of the free radical was 100 mM).…”

“…The obtained solid (1.02 g) was crystalized from ethanol (80–90 mL) leading to the product as bright yellow crystals (0.8 g, 78%). The spectral data of the compound correspond to those given in literature .…”

“…Compounds 1 a‐d , 1 e , 1 f , 1 g,h , 1 i , 1 k , 1 l , 1 m , 1 o , 1 p , 1 q,r , 1 s , 1 t , 2 , 3 , 4 , and 14 are known and their 1 H NMR spectra correspond to literature.…”

Crystal structure of 5-[4-(diethylamino)benzylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione

“…Mohite & Bhat, 2013). Arylidene Meldrum's acids can be easily converted to arylmethyl Meldrum's acids [for a description of a typical procedure, see Mierina et al (2015)], which serve as starting compounds for the synthesis of various valuable compounds [for a mini-review, see Mierina (2014)]. Apart from their wide application in syntheses, these derivatives of Meldrum's acid have been studied as platelet aggregation inhibitors (El Maatougui et al, 2012), antimalarial agents and anti-oxidants (Sandhu et al, 2010) and photostable UV-filters for cosmetic applications (Habeck & Krause, 1999).…”