Ideally selective diisocyanate building blocks: New perspectives for dendrimers and coating binders

Using zirconium (IV) salts as catalyst, the reaction of a diisocyanate carrying one tertiary and one primary isocyanate group (IMCI, DIMP) with alcohols can be conducted with complete regioselectivity. This unique selectivity enables the use of a diisocyanate building block in unprecedented ways. Incomplete regioselectivity of diisocyanates, as commonly encountered in currently commercial ones like IPDI and TDI, inevitably leads to polydisperse products in reaction with polyols. The ultimate monodisperse polymer architecture, dendrimers, can now be made in a facile, straightforward manner using IMCI as the ideal diisocyanate building block. Coating applications of this unique building block are not restricted to these perfect branching polymers, but also include isocyanate-functional coating resins. Without any increase in polydispersity, a hydroxyl-functional polyester can be end-capped with the IMCI diisocyanate and subsequently serve as a crosslinker in powder coatings.     

Understanding the molecular mechanism and regioselectivity in the synthesis of celecoxib via a domino reaction: A DFT study

The molecular mechanism and energetic of the domino reaction involved in the synthesis of celecoxib, a well-known anti-inflammatory drug, were theoretically studied at the DFT-B3LYP/6-31G^* level. The first reaction in this domino process, which is also the rate-determining step, is a complete regioselective [3 + 2] cycloaddition (32CA) reaction associated with the nucleophilic attack of C5 carbon atom of enamine 7 on the C3 carbon atom of nitrile imine 6, leading to cycloadduct 8. The second reaction is a rapid acid/base catalysed stepwise elimination reaction of the morpholine 9 from cycloadduct 8 affording celecoxibe 3. The results also show that neither molecular mechanism of reaction nor activation barriers are considerably affected by the inclusion of solvent. The calculated relative Gibbs free energies as well as local reactivity indices obtained using the calculated Parr functions explain the complete regioselective fashion provided by the 32CA reaction under consideration in excellent agreement with the experimental findings.     

Catalysis for fine chemicals: towards specificity with polyphasic media

Three examples of the work undertaken at the Institut de Recherches sur la Catalyse for the selective preparation of fine chemicals in polyphasic media are presented and discussed:

1. diastereoselective hydrogenation of 1,2-disubstituted arenes to cyclohexyl derivatives,

2. chemoselective oxidation of anilines, and

3. regioselective alkoxycarbonylation of styrene derivatives to 2-arylpropionic esters.

Factors influencing the selectivity of these reactions are discussed in the light of concepts from molecular chemistry.     

Platinum group metals as catalysts in enantioselective 1-phenylpropane-1,2-dione hydrogenation

Different γ-Al₂O₃ supported Ir, Pd, Ru, Rh and Pt catalysts were tested in enantioselective 1-phenylpropane-1,2-dione hydrogenation using cinchona alkaloid modifiers. Activity and enantioselectivity over Ir and Ru catalysts were low. Pd catalyst was active in the hydrogenation of 1-phenylpropane-1,2-dione, however, the enantioselectivity over this catalyst was almost negligible. Over Pd hydrogenation proceeded mainly via hydrogenation of the C₁O₁ carbonyl group, which is attached to the phenyl ring. Hydrogenation over Pd did not proceed in the second hydrogenation step via an enol form as found for ethyl pyruvate hydrogenation over Pd. The structure-selectivity relationship and solvent effects are similar over Pt and Rh in the first hydrogenation step. However, in the second hydrogenation step of hydroxyketones to diols large mechanistical differences between Pt and Rh were observed. Although the activity over Rh catalysts was lower than over Pt after optimization the best result obtained with Rh/γ-Al₂O₃ (5754 Lancaster) was 60% ee in toluene at maximum yield of 28%, which makes Rh a promising metal for enantioselective hydrogenation.     

Electrosynthesis using a fluoride ion mediator. Part V: Fluoride ion mediated anodic methoxylation and acetoxylation of thiazolidines, 1,3-oxathiolanes, and 1,3-dithiolanes

Anodic methoxylation and acetoxylation reactions of five membered cyclic sulfides such as thiazolidines, 1,3-oxathiolanes and 1,3-dithiolanes, which have been reported to not always undergo the Pummerer reaction, were successfully carried out by using a fluoride ion mediator.     

酸性皂土催化剂作用下硝酸硝化卤苯的区域选择性

芳烃硝化的现实意义之一是建立具有区域选择性的硝化方法以满足质量的发展要求。在酸性皂土催化剂上 ,应用硝酸硝化卤苯能够提高卤苯的对位选择性硝化能力 ,氟苯、氯苯、溴苯和碘苯的邻对硝基异构体比例分别为 0 .1 3、0 .2 9、0 .33和 0 .42     

A rapid regioselective ring-opening of aziridines with potassium thiocyanate using ammonium-12-molybdophosphate

Ammonium-12-molybdophosphate, a heterogeneous catalyst, has been utilized for the first time for rapid (within 15–20 min) regioselective ring-opening of aziridines with KSCN at room temperature to form the corresponding β-aminothiocyanates in high yields.     

Catalytic Mononitration of Phenol Using <Emphasis Type="Italic">iso-</Emphasis>Propyl Nitrate Over Zeolite Catalysts

Mononitration of phenol was investigated using iso-propyl nitrate as a nitrating agent over various zeolite catalysts under different reaction conditions. Zeolite Hβ with a low Si/Al ratio (12.5) was found to be an active catalyst for nitration of phenol under reflux conditions in dichloroethane, producing 2- and 4-nitrophenols in a ratio of around 1:1. However, zeolites H-mordenite, HY and Hβ (with high Si/Al ratio—150 or 300) gave 2-nitrophenol as the major product (ortho/para ratio = ca. 2–3).     

Synthesis, structures and thermal properties of new class epoxide-terminated telechelic poly(2,6-dimethyl-1,4-phenylene oxide)s

Dihydroxyl telechelic poly(2,6-dimethyl-1,4-phenylene oxide)s (1) with regiocontrolled end-group structures have been synthesized by oxidative polymerization of 2,6-dimethylphenol with various aromatic diols in the presence of CuBr/dibutylamine catalysts. The novel one- or two-armed telechelic derivatives based on aromatic diols as core and 1 as arms were subsequently epoxidized with epichlorohydrin and a series of new epoxidized poly(2,6-dimethyl-1,4-phenylene oxide)s (2) were accessible with number average molecular weight ranged from 3500 to 14,000. The end-group structures and regioselectivity of polymers were controlled by the CuBr/dibutylamine catalysts under different reaction conditions, and the structures and properties were studied by nuclear magnetic resonance spectroscopy, gel permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. Upon heating in the presence of oxygen, the one-armed dihydroxyl telechelic polymer was converted via intermolecular coupling and redistribution reaction to the two-armed derivative with significant increase in its molecular weight and elimination of diol monomer. Treatment of dihydroxyl telechelic derivatives with epichlorohydrin and NaOH afforded the epoxide-terminated telechelic derivatives in 77-94% yields.