Non-isocyanate polyurethanes (NIPUs) constitute a promising alternative for more classical polyurethanes (PUs) as they may display mechanical properties that can match those of PUs and their synthesis does not involve the use of toxic isocyanates. Yet, because of the lower reactivity of carbonates versus isocyanates, the synthesis of NIPUs is not straightforward and generally requires the use of a catalyst. Recently, several groups have reported on the use of different ranges of catalysts for promoting the nucleophilic attack of the amine on the carbonate. However, many of these studies involve the use of highly reactive amine and/or carbonate proscribing a complete panorama of the potentialities of the reaction. Herein, we propose a rational study of the catalyzed aminolysis of four representative cyclic carbonates that reveals that the thiourea organocatalyst 1 outperforms in many aspects, classical inorganic or other organic catalysts.

The intent of this tutorial review is to cover the recent progress accomplished in iron and manganese porphyrin-catalyzed enantioselective epoxidation of terminal olefins. The literature is covered up to the beginning of 2005. In the first part of the manuscript, we will present the results obtained with simple catalysts in the early eighties, before describing the pickets and strapped series reported more recently. We will also place a special emphasis on the biomimetic approach that oriented most of this research throughout the years. As a conclusion, we will demonstrate that easy-to-prepare porphyrin catalysts should play an important role in the future and should compete with other well-known, successful systems. Among those, the popular titanium tartrate-catalyzed Sharpless-Katsuki asymmetric epoxidation allows the conversion of allylic alcohols to chiral epoxides with high enantiomeric excesses and high conversion. We will also cite the chiral metallosalen complexes independently reported by Jacobsen and Katsuki in 1990. Using manganese-salens, cis-1,2-disubstituted, trisubstituted and some tetrasubstituted olefins are efficiently epoxidized with high enantiomeric excess. However, they suffer from two major drawbacks. They often require low temperature for the epoxidation of monosubstituted (57% ee for styrene at 5 degrees C; 80% at -78 degrees C). More importantly, they proceed with low turnover numbers, TON (TON approximately 40 for styrene). More recently, a new approach involving metal-free chiral dioxiranes was also reported. In some cases, they constitute an interesting alternative to the more common systems previously discussed. Compared to the three pre-cited systems, chiral metalloporphyrins allow the enantioselective epoxidation of unfunctionalized terminal olefins with high enantiomeric excess (>97% ee for styrene) and impressive turnover numbers (>16000) when PhIO is used as oxidant. These results highlight the remarkable potential of porphyrin-based catalysts.

In recent years, intensive research and development have been carried out for the synthesis of isocyanate free polyurethanes from the reaction between five-membered cyclic carbonates and amines to yield polyhydroxyurethanes (PHU). Nevertheless, this reaction presents two main drawbacks: the low reactivity of cyclic carbonate aminolysis and the low molar masses of synthesized PHUs. Firstly, our work intends to propose a wider reactivity study on various C₅ and C₆ in order to determine the influence of substituents attached to the cyclic carbonate and to compare the reactivity of C₅ and C₆ with exactly the same substituents. Moreover, we completed this study with new structures with promising reactivity such as C₅ and C₆ with ethyl-ester or trimethylhexanoate substituents that have never been studied in the literature. Hence, a range of cyclic carbonate models with different structures, 5-, 6-membered cyclic carbonate (C₅, C₆) or 5-membered-dithio-cyclic carbonate (C_s), were synthesized. Secondly, this kinetic study has brought to light a partial conversion of precursors during the aminolysis reaction that can be responsible for the low molar masses of PHUs. This partial conversion is caused mainly by the formation of hydrogen bonding inter- and intra-chains limiting the diffusivity of species during the polymerization. A model study showed that the use of protic solvents improves the reactivity of cyclic carbonates and increases the conversion during their aminolysis reaction. Therefore, this protic solvent gives its mobility back to the precursors by limiting the creation of hydrogen bonding inter- and intra-chains. Finally, the efficiency of protic solvents on the synthesis of PHU polymers was evaluated.

Calixphyrins are a class of hybrid molecules that lie at the structural crossroads between porphyrins and calixpyrroles. Porphyrins, long known for their versatile metal cation coordination chemistry, are macrocycles that contain only sp2-hybridized bridging meso carbon atoms within their framework. Calix[n]pyrroles, on the other hand, are porphyrin analogs that contain pyrroles bridged exclusively by sp3 meso carbon centers, and in recent years have been shown to display remarkable anion-binding properties. Calix[n]phyrins bear analogy to both the porphyrins and calixpyrroles and are macrocyclic analogs that contain a mixture of sp2- and sp3-hybridized meso carbon bridges. This leads to partial interruptions in the conjugation pathway of the molecule, introduces novel structural features, and leads to interesting anion and cation recognition properties. It also allows for modular syntheses. In the present paper, the chemistry of calix[n]phyrins, still at an early stage of exploration, is reviewed.