On Tautomerism and Amphoterism: An In-Depth Structural and Physicochemical Characterization of Ammeline and Some of Its Salts.

Ammeline is a simple, readily available, molecular compound, which has been known for nearly 200 years. Despite that, no proper structural characterization of ammeline has been conducted so far. For this reason, the prevalent tautomeric form of ammeline in the solid remained unknown to this date. In the course of this study, its crystal structure was finally established by single-crystal X-ray diffraction. In this structure, ammeline is exclusively found as its 4,6-diamino-1,3,5-triazin-2(1H)-one tautomer and adopts layered structure with an exceptionally high hydrogen bond density. Ammeline shows an interesting amphoteric behavior. Therefore, the synthesis and structural characterization of some of its salts were carried out to investigate the influence of the protonation degree on its molecular structure. In particular, the crystal structure of silver ammelinate monohydrate was solved as the first reported structure containing deprotonated ammeline. Moreover, the crystal structures of three different modifications of ammelinium perchlorate were elucidated and the transformation conditions between them were studied. Lastly, the crystal structure of ammelinediium diperchlorate monohydrate, containing unprecedented doubly protonated ammeline, was determined. The products' thermal behavior was studied by differential thermal analysis and thermogravimetric analysis. The perchlorate salts were additionally examined for their potential as insensitive high-energy-density materials.

Simple Molecules under High-Pressure and High-Temperature Conditions: Synthesis and Characterization of α- and ß-C(NH)2 with Fully sp3 -Hybridized Carbon.

The elements hydrogen, carbon, and nitrogen are among the most abundant in the solar system. Still, little is known about the ternary compounds these elements can form under the high-pressure and high-temperature conditions found in the outer planets' interiors. These materials are also of significant research interest since they are predicted to feature many desirable properties such as high thermal conductivity and hardness due to strong covalent bonding networks. In this study, the high-pressure high-temperature reaction behavior of malononitrile H2 C(CN)2 , dicyandiamide (H2 N)2 C=NCN, and melamine (C3 N3 )(NH2 )3 was investigated in laser-heated diamond anvil cells. Two previously unknown compounds, namely α-C(NH)2 and ß-C(NH)2 , have been synthesized and found to have fully sp3 -hybridized carbon atoms. α-C(NH)2 crystallizes in a distorted ß-cristobalite structure, while ß-C(NH)2 is built from previously unknown imide-bridged 2,4,6,8,9,10-hexaazaadamantane units, which form two independent interpenetrating diamond-like networks. Their stability domains and compressibility were studied, for which supporting density functional theory calculations were performed.

Pyrrole-Protected ß-Aminoalkylzinc Reagents for the Enantioselective Synthesis of Amino-Derivatives.

Chiral ß-aminoalkylzinc halides were prepared starting from optically pure commercial ß-amino-alcohols. These amino-alcohols were converted to the corresponding N-pyrrolyl-protected alkyl iodides which undergo a zinc insertion in the presence of LiCl (THF, 25 °C, 10-90 min). Subsequent Negishi cross-coupling or acylation reactions with acid chlorides produced amino-derivatives with retention of chirality. Diastereoselective CBS-reductions of some prepared N-pyrrolyl-ketones provided 1,3-subsituted N-pyrrolyl-alcohols with high diastereoselectivity. Additionally, a deprotection procedure involving an ozonolysis allowed the conversion of the pyrrole-ring into a formamide without loss of optical purity.

Copper-Catalyzed Electrophilic Thiolation of Organozinc Halides by Using N-Thiophthalimides Leading to Polyfunctional Thioethers.

(Hetero)aryl, benzylic, and alkyl zinc halides were thiolated with N-thiophthalimides at 25 °C within 1 h in the presence of 5-10 % Cu(OAc)2 ⋅H2 O to furnish the corresponding polyfunctionalized thioethers in good yields. This electrophilic thiolation was extended to the introduction of trifluoromethylthio (SCF3 ), thiocyanate (SCN), and selenophenyl (SePh) groups. The utility of this method was shown in a seven-step synthesis of a potent cathepsin D inhibitor in 34 % overall yield.