Imidazole-1-sulfonyl Azide-Based Diazo-Transfer Reaction for the Preparation of Azido Solid Supports for Solid-Phase Synthesis (original) (raw)
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Diazo transfer for azido-functional surfaces
Materials Today, 2011
Preparation of azido-functionalized polymers is gaining increasing attention. We wish to report an innovative, novel strategy for azido functionalization of polymeric materials, coupling plasma technology and solution processed diazo transfer reactions. This novel approach allows the azido group to be introduced downstream of the material preparation, thus preserving its physicochemical and mechanical characteristics, which can be tailored a priori according to the desired application. The whole process involves the surface plasma functionalization of a material with primary amino groups, followed by a diazo transfer reaction, which converts the amino functionalities into azido groups that can be exploited for further chemoselective reactions. The diazo transfer reaction is performed in a heterogeneous phase, where the azido group donor is in solution. Chemical reactivity of the azido functionalities was verified by subsequent copper-catalyzed azide-alkyne cycloaddition.
Development of the Traceless Phenylhydrazide Linker for Solid-Phase Synthesis
Chemistry - A European Journal, 2003
The hydrazide group is a new oxidatively cleavable traceless linker for solid-phase chemistry. It can be readily introduced by hydrazide formation between a carboxy-functionalized resin and different substituted hydrazines. In order to achieve high yields in this step, new carboxylic acid resins were developed that are not prone to undesired imide formation upon activation of the carboxylic acid. The polymer-bound acyl hydrazides were successfully employed in various transformations, namely Heck, Suzuki, Sonogashira, and Stille couplings, as well as Wittig and Grignard reactions. Traceless release of the coupling products from the solid support is achieved selectively under mild conditions and in high purity by oxidation of the aryl hydrazides to acyl diazenes with Cu II salts or N-bromosuccinimide (NBS) and subsequent nucleophilic attack of the acyl diazene intermediates. Traceless cleavage by oxidation with NBS can be carried out as a two-step process in which stable acyl diazenes are first generated by treatment with NBS in the absence of a nucleophile. After removal of the reagents by simple resin washing, the traceless release is effected by the addition of methanol, which leads to products of high purity without any additional separation steps.
Azide telechelics chain extended by click reaction: Synthesis, characterization, and cross-linking
Polymers for Advanced Technologies, 2018
These oligomeric azides were chain extended by reaction with bispropargyl ether of bisphenol A (BPEBA) through a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. PDMS manifested a faster reaction in contrast to PPO or PEO. The chain-extended polymers underwent cross-linking above 170°C through thermal cleavage of residual (terminal) azide groups. This was manifested in their rheograms and was further substantiated by FTIR and NMR spectroscopic analyses. Dynamic mechanical analyses of the cross-linked polymers exhibited characteristic transitions of hard and soft segments, implying microphase separation in the system. Microscopic evaluation of the thermally cross-linked sample revealed a porous morphology with microsized to nanosized pores.
Herein, we present the first examples of solvent-assisted linker exchange (SALE) in zeolitic imidazolate frameworks (ZIFs). By exposing the ZIF CdIF-4 to excess solutions of 2-nitroimidazole and 2-methylimidazole under solvothermal conditions, we were able to obtain a previously reported ZIF CdIF-9 in high yield, as well as synthesize a new ZIF, Solvent-Assisted Linker-Exchanged Material-1 (SALEM-1). The parent and daughter ZIFs are isostructural (RHO zeolitic topology) and highly porous. Despite the high thermal and chemical stability of ZIFs, single crystal-to-single crystal linker exchange appears to be a suitable tool for the modification and functionalization of these materials. We anticipate that the addition of SALE to the arsenal of known synthetic techniques for ZIFs will significantly facilitate the quest to obtain interesting and useful ZIF compounds, including compounds that cannot be synthesized directly.
One Pot Synthesis of Imidazole-Triazole Framework via Dimorth Rearrangement and Click Reaction
There are only a few approaches that describe the direct synthesis of 2-aminoimidazoles and their biological activity 1-5. The earliest method involves condensation of α-aminocarbonyl compounds with cyanamide or their synthetic equivalents 6, 7. This method is most commonly used for the direct construction of the 2-aminoimidazole ring. Other general applicable strategies are cyclocondensation of α-bromoketone with N-acetylguanidine in acetonitrile 8 , iminophosphorane-mediated cyclization of α –azido esters 9 , ammonolysis of 2-amino-1,3-oxazol-3-iumsalts 10 , sequential functionalization of 1,2-diprotected imidazole ring with different electrophiles 11. Most of them involve long experimental procedures, the use of unstable precursors and tiresome workup process. Accordingly, the development of straightforward and general procedures for the synthesis of diversely substituted 2-aminoimidazoles from readily available precursors is highly warranted. Herein, we report a rapid and highly efficient Cu-mediated synthesis of 2-aminoimidazoletriazole framework via click reaction and dimorth rearrangement. ―Click chemistry‖ has emerged as a fast and efficient approach to synthesis of novel compounds with desired function making use of selected ―near perfect‖ reactions. 12 (very fast, selective, high-yield, and wide scope) The Dimroth rearrangement 13 is an isomerization of heterocycles that consists in a translocation of endo-or exocyclic heteroatoms through a ring-opening-ring-closure sequence. It can be catalyzed by acids, bases, heat or light. Recently group of Erik 14 reported a new one pot microwave assisted synthesis of substituted 2-amino-1H-imidazoles from readily available 2-aminopyrimidine (1) and α-bromoketone (2). The first step was performed by heating N-(3-azidopropyl)pyrimidin-2-amine (1) and 2-bromo-1-phenylethanone (2) at 75°C for 3 h resulting in the formation of hydroxyl salt (3) which undergoes dimorth type rearrangement by 7 equiv of NH2NH2.H2O resulting in the formation of N-(2-azido)-1H-imidazol-2-amine. Final step of click reaction was performed under microwave irradiation using phenylacetylene (1.5.equiv), Cu(Oac)2 (10 mol %)as catalyst at 100°C 10 min with a maximum power of 40W to obtain 2-AI-T scaffold (5). (Scheme 1)
Journal of Combinatorial Chemistry, 2009
The development of new therapeutic agents, as well as the identification of molecular probes for the study of the chemical/biological interfaces, is one of the major goals in biomedical research. In this context, the availability of large libraries of small organic molecules, covering as much chemical space as possible, is seen as the only means which guarantees potential modulation of the many biological targets that are ultimately being unveiled by genomics. 1 Therefore, advances in drug discovery depend heavily on the availability of synthetic transformations that allow the rapid assembly of complex molecular frameworks providing maximum diversity. Low molecular weight nitrogen containing heterocycles are securing their place among the most highly recognized pharmacophores. 2 Among them, the benzo fused imidazoles, oxazoles, and thiazoles are of particular interest, since they are well-known to exhibit a broad range of biological activities. 3 They are also showing interesting utility in advanced material science such as nonlinear optics (NLO), 4 organic light-emitting diodes (OLED), 5 and liquid crystals. 6 Consequently, benzimidazoles and benzoxa/(thia)zoles are prized as potential drug candidate and biological probes (Figure 1). The retro-synthesis of these heterocycles suggests that they could be synthesized by coupling of the amine component 1 and aldehyde or acid derivative component 2 (Figure 2). Polymer-supported combinatorial chemistry is an efficient methodology for the construction of compound libraries and has been applied to drug discovery, catalyst development, and material science. 7 The use of a polymeric support in combinatorial chemistry facilitates handling and purification of polymer-bound intermediates and separation of products. 8 Another important advantage of using solid supported reagents is that the solid support can easily be filtered off, recovered, and reused. This is environmentally safe. There are a few reports related to the synthesis of functionalized benzimidazoles, benzoxazoles, and ben
Bulletin of the Korean Chemical Society, 2012
An efficient solid-phase methodology has been developed for the synthesis of 2-amino and 2-amidobenzo[d]oxazole derivatives. The key step in this procedure involves the preparation of polymer-bound 2-aminobenzo-[d]oxazole resins 4 by cyclization reaction of 2-hydroxyphenylthiourea resin 3. The resin-bound 2-hydroxyphenylthiourea 3 is produced by the addition of 2-aminophenol to the isothiocyanate-terminated resin 2 and serve as a key intermediate for the linker resin. This core skeleton 2-aminobenzo[d]oxazole resin 4 undergoes functionalization reaction with various electrophiles, such as alkylhalides and acid chlorides to generate 2amino and 2-amidobenzo[d]oxazole resins 5 and 6 respectively. Finally, 2-amino and 2-amidobenzo[d]oxazole derivatives 7 and 8 are then generated in good yields and purities by cleavage of the respective resins 5 and 6 under trifluoroacetic acid (TFA) in dichloromethane (CH 2 Cl 2).