Ahmed Al-Sheikh

Novel Derivatives of 1,3-Dimethyl-5-methylenebarbituric Acid

The ability of the pyridinium adduct of 1,3-dimethyl-5-methylenebarbituric acid (2) to undergo nucleophilic substitution reaction has been examined. Various types of nucleophiles, including cyanide, barbiturate, sulfide anions and 1,2-bis(diphenylphosphino)ethane substitute the pyridinium fragment in 2 leading to synthesis of new organic derivatives.

Synthesis of Phosphorus, Arsenic and Antimony Ylides Containing the 1,3- Dimethyl-2,4,6(1H,3H,5H)-pyrimidinetrione Fragments

The ylides Ph3E-C6H6N2O3 (7, E = P (a), As (b), Sb (c)) have been prepared through the reaction of Ph3E and 5- bromo-1,3-dimethyl-2,4,6(1H,3H,5H)-pyrimidinetrione (5-bromo-1,3-dimethylbarbituric acid) 6 in the presence of trieth- ylamine. Their characterisation was performed by nuclear magnetic resonance (NMR), mass spectrometry (MS) and ele- mental analysis.

Crystal structure of 5-[bis-(methyl-sulfon-yl)meth-yl]-1,3-dimethyl-5-(methyl-sulfon-yl)pyrimidine-2,4,6(1H,3H,5H)-trione.

In the title compound, C10H16N2O9S3, the pyrimidine ring of the 1,3-dimethyl barbituric acid moiety has an envelope conformation with the C atom carrying the methylsulfonyl and bis(methylsulfonyl)methyl substituents as the flap. The dihedral angle between mean plane of the pyrimidine ring and the S/C/S plane is 72.4 (3)°. In the crystal, molecules are linked via C—H⋯O hydrogen bonds, forming a three-dimensional structure.

Zur Strukturchemie von 2-Methylenimidazolinen [1]

The 2-methylenimidazolines ImC(CN)2 (6a - c, Im = 1,3-dialkyl-4,5-dimethylimidazol-2-ylidene) are prepared by the reaction of the imidazolium salts [ImBr]Br (5) and malodinitrile while ImC{C(O)Ph}2 (7) is obtained from ImCH2 (2) and benzoic fluoride. Both the structural data of 6b, 6c, and 7 and the 13C NMR data demonstrate the influence of steric and electronic effects on the charge separation and the nonplanar arrangement of the substituents attached at the carbon atoms of the central olefinic bond

Zur Reaktion von 2,3-Dihydro-1,3-diisopropy1-4,5-imidazol-2-yliden mit Bromderivaten der Meldrumsäure [1, 2] / On the Reaction of 2,3-Dihydro-1,3-diisopropy1-4,5-dimethylimidazol-2-ylidene with Bromine Derivatives of Meldrum’s Acid [1, 2]

The Imidazolium salts [ImH][MelBr] (7) and [ImBr][MelBr] (8) have been obtained from the carbene Im (5) and the Meldrum’s acid derivatives MelHBr (3) and MelBr2 (4). The crystal structure analyses of 7 and 8 reveal the presence of ion pairs linked by short OH (7: 2.163 Å ) and OBr (8: 2.872 Å ) contacts.

Synthese und Struktur von Meldrums Olefin/Synthesis and Structure of Meldrum’s Olefin

Abstract Diisopropylidene ethylenetetracarboxylate, Meldrum’s olefin (4, Mel2) has been prepared from [HNEt3][(Mel)2CSMe] (8) and Meldrum’s acid (1, MelH2) in moderate yield. The X-ray analysis of 4 reveals a centrosymmetrical structure in which the two six-membered rings are folded along their carboxylate carbon axes by 34.9°) and linked by a conventional C-C double bond [1.3501(19) Å ]. The “unsymmetrical” structure of 8 is also discussed.

2-Amino-1,3-dimethylimidazolium 2,2-dimethyl-4,6-dioxo-1,3-dioxanide. First structural characterisation of the anion of Meldrum's acid [1]

2-Amino-1,3-dimethylimidazolium 2,2-dimethyl- 4,6-dioxo-1,3-dioxanide (6) has been obtained from the reaction of 2,2-dimethyl-4,6-dioxo-1,3- dioxan (1, “Meldrum’s acid”) and 2-imino-1,3-dimethylimidazoline (5) in excellent yield. The unit cell of 6 contains two crystallographically independent anions lying on crystallographic mirror planes. The structure of the anion is compared with that of compound 1.

Synthesis and Structure of 1-{2,2-Dimethyl-4,6-dioxo-5-(1-pyridinio)-1,3- dioxan-5-yl}pyridinium Ylide: A New Route to Meldrum's Acid Derivatives

2-Bromo-5,5-dimethyl-4,6-dioxo-1,3-dioxine (3) reacts with pyridine and aqueous potassium carbonate to give 1-{2,2-dimethyl-4,6-dioxo-5-(1-pyridinio)-1,3-dioxan-5-yl}pyridinium ylide (5). The crystal structure analysis confirms the betaine nature of 5 consisting of two distored ring fragments [interplanar angle 58.0(4)°] connected by a C-N single bond [1.440(1) Å ].