In this microreview, we highlight the field of polymer‐supported organocatalysis, especially immobilized enamine and iminium organocatalysts. We try to formalize the overall synthetic strategies for polymeric immobilization as spanning the area of two overlapping regions, from a copolymer strategy favoured by low‐valued and small catalysts to a classical post‐modification strategy favoured by valuable and/or large catalysts. Organocatalysis is particularly interesting as it is probably best described as being located in the transitional region, and we will trace the historic and factual origins for the unfortunate predispositions towards post‐modification schemes. In addition, we try to identify affordable and useful syntheses of key organocatalyst immobilization intermediates, as well as polymer supports that are more compatible with a broader range of reaction solvent polarity, something of crucial importance in organocatalysis.

Polymer-supported chiral organocatalysts, as well as most other forms of immobilized catalysts, are traditionally prepared by a postmodification approach where modified catalyst precursors are anchored onto prefabricated polymer beads. Herein, we report an alternative and more scalable approach where polymer-supported chiral enamine and iminium organocatalysts are prepared in a bottom-up fashion where methacrylic functional monomers are prepared in an entirely nonchromatographic manner and subsequently copolymerized with suitable comonomers to give cross-linked polymer beads. All syntheses have been conducted on multigram scale for all intermediates and finished polymer products, and the catalysts have proven successful in reactions taking place in solvents spanning a wide range of solvent polarity. While polymer-supported proline and prolineamides generally demonstrated excellent results and recycling robustness in asymmetric aldol reactions of ketones and benzaldehydes, the simplest type of Jørgensen/Hayashi diarylprolinol TMS-ether showed excellent selectivity, but rather sluggish reactivity in the Enders-type asymmetric cascade. The polymer-supported version of the first-generation MacMillan imidazolidinone had a pattern of reactivity very similar to that of the monomeric catalyst, but is too unstable to allow recycling.

Very few efficient bonding agents for use in solid rocket propellants with nitramine filler materials and energetic binder systems are currently available. In this work, we report the synthesis, detailed characterization, and use of neutral polymeric bonding agents (NPBA) in isocyanate‐cured and smokeless composite rocket propellants based on the nitramine octogen (HMX), the energetic binder glycidyl azide polymer (GAP), and the energetic plasticizer N‐butyl‐2‐nitratoethylnitramine (BuNENA). These polymeric bonding agents clearly influenced the viscosity of the uncured propellant mixtures and provided significantly enhanced mechanical properties to the cured propellants, even at low NPBA concentrations (down to 0.001 wt‐% of propellant). A modified NPBA more or less free of hydroxyl functionalities for interactions with isocyanate curing agent provided the same level of mechanical improvement as regular NPBA containing a substantial number of reactive hydroxyl groups. However, some degree of reactivity towards isocyanate is essential for function.

A completely non-chromatographic and highly large-scale adaptable synthesis of acrylic polymer beads containing proline and prolineamides has been developed. Novel monomeric proline (meth)acrylates are prepared from hydroxyproline in only one step. Free-radical copolymerization then gives solid-supported proline organocatalysts directly in as little as two steps overall, without using any prefabricated solid supports, by using either droplet or dispersion polymerization. These affordable acrylic beads have highly favorable and adjustable swelling characteristics and are excellent reusable catalysts for organocatalytic reactions.

Traditional composite rocket propellants are cured by treatment of hydroxyl‐terminated prepolymers with polyfunctional aliphatic isocyanates. For development of smokeless composite propellants containing nitramines and/or ammonium dinitramide (ADN), energetic binder systems using glycidyl azide polymer (GAP) are of particular interest. Polyfunctional alkynes are potential isocyanate‐free curing agents for GAP through thermal azide‐alkyne cycloaddition and subsequent formation of triazole crosslinkages. Propargyl succinate or closely related aliphatic derivatives have previously been reported for such isocyanate‐free curing of GAP. Herein, we present the synthesis and use of a new aromatic alkyne curing agent, the crystalline solid bisphenol A bis(propargyl ether) (BABE), as isocyanate‐free curing agent in smokeless propellants based on GAP, using either octogen (HMX) and/or prilled ADN as energetic filler materials. Thermal and mechanical properties, impact and friction sensitivity and ballistic characteristics were evaluated for these alkyne cured propellants. Improved mechanical properties could be obtained by combining isocyanate and alkyne curing agents (dual curing), a combination that imparted better mechanical properties in the cured propellants than either curing system did individually. The addition of a neutral polymeric bonding agent (NPBA) for improvement of binder‐filler interactions was also investigated using tensile testing and dynamic mechanical analysis (DMA). It was verified that the presence of isocyanates is essential for the NPBA to improve the mechanical properties of the propellants, further strengthening the attractiveness of dual cure systems.

In this work we show how a direct O-acylation of trans-4-hydroxy-L-proline with acyl chlorides in trifluoroacetic acid makes a range of novel proline derivatives readily available on large-scale. No protecting groups or chromatographic techniques are involved in any of the procedures, and certain amphiphilic proline derivatives, which recently have received interest in synthesis, are now potentially some of the

a] 1I ntroductionIn solid propellant rocketry,p ropulsion units in fielded and currently operational missile systems are founded upon ar elatively small number of firmly established propellant technologies, most of which have an extensive historical track record. While propulsion systems with either limited or no restrictions with respect to exhaust plume signature have their basis in ammonium perchlorate (AP) composites with inert binder systems (preferably aluminized), smokeless systems are based on nitrate ester plasticized binders (nitrocellulose, polyethers, polyesters) with or without nitramine filler materials [1].C ombination of the two sorts gives rise to the high-performance propellant types important in domains such as submarine-launched ballistic missiles, applications where performance with regards to specific impulse is particularly critical [2].Although implemented propellant technology has now remained somewhat static for ac onsiderable period of time, new incentives have accelerated the development of new generations of solid rocket propellants. Increasingly stringent legislature associated with the handling and use of many chemical species traditionally used in rocket propellant formulations (heavy metal compounds, perchlorates, isocyanates), when assessed in conjuncture with at ightening export bureaucracy and the diminishing production base for many important raw materials (a result of plant closures and industry consolidation during recent decades), have all contributed to an increased willingness by relevant manufacturers to evaluate new propellant candidates.The bulk of contemporary research efforts directed towards new solid rocket propellant candidates is concentrated around new energetic binder systems and chlorine-free filler materials, as well as associated formulation additives (curing agents, bonding agents, burning rate modifiers) [3-Abstract:G lycidyl azide polymer (GAP) is an important energetic binder candidate for new minimum signature solid composite rocket propellants, but the mechanical properties of such GAP propellants are often limited. The mechanical characteristics of composite rocket propellants are mainly determined by the nature of the binder system and the binder-filler interactions. In this work, we report ad etailed investigation into curing systems for GAP diol with the objective of attaining the best possible mechanical characteristics as evaluated by uniaxial tensile testing of non-plasticized polymer specimens. We started out by investigating isocyanate and isocyanate-free curing systems, the latter by using the crystalline and easily soluble alkyne curing agent bispropargylhydroquinone (BPHQ). In the course of the presented study,w et hen assessed the feasi-bility of dual curing systems, either by using BPHQ and isophorone diisocyanate (IPDI) simultaneously (synchronous dual curing), or by applying propargyl alcohol and IPDI consecutively (sequential dual curing). The latter method, which employs propargyl alcohol as ar eadily available and adjustable hydroxyl...

In this work we present new, fully synthetic phenylglycine‐derived primary amine organocatalysts useful for the one‐step preparation of optically active warfarin, an important anticoagulant. Both enantiomeric forms of the catalysts are equally available and can be prepared by robust procedures without recourse to chromatographic purification. Together with a co‐catalyst, particularly acetic acid or 2,4‐dinitrophenol, they can furnish warfarin in approximately 80 % ee and represent inexpensive alternatives to other primary amine organocatalysts such as the chiral diamines and Cinchona‐derived primary amines.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)