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Rhodium(II)-acetate-catalyzed decomposition of either 1,3-cyclohexanedione phenyliodonium ylide or 5,5-dimethyl-1,3-cyclohexanedione phenyliodonium ylide in the presence of alkyl halides yields the corresponding 3-alkoxy-2-halocyclohex-2-enones via a 1,4 alkyl group migration shown to be concerted and intramolecular. In the case of (S)-alpha-phenethyl chloride, the rearrangement proceeds with essentially 88.6% retention of configuration. Theoretical calculations at the B3LYP/6-31G level reveal an activation energy of 5.4 kcal/mol for the process. A Claisen-like rearrangement occurs in the case where allylic halides, such as dimethylallyl or methallyl chorides, are used. The mechanistic pathway proposed for these processes involves addition of the halogen atom of the alkyl or allyl halide to the rhodium carbenoid from the iodonium ylide to yield a halonium intermediate that undergoes halogen to oxygen group migration. Aryl halides, such as chloro-, bromo-, iodo-, and fluorobenzene, behave differently under the same reaction conditions, yielding the product of electrophilic aromatic substitution, namely, the 2-(4-halophenyl) 1,3-cyclohexanedione.

New hybrid cryogels comprising natural polymers (free atelocollagen or atelocollagen mixed with a hyaluronic acid derivative) and a synthetic polyester--poly(ε-caprolactone)--were successfully developed by a cryogenic treatment and a subsequent freeze-drying step. Systematic studies on the effect of preparation conditions (reaction mixture composition, total concentration of the feed dispersion, and freezing regime) on cryogelation efficiency were conducted. The degree of cross-linking and the morphology of the obtained materials were analyzed using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and (environmental) scanning electron microscopy (ESEM/SEM) techniques. Considering their possible biomedical application, the developed macroporous hydrogels were also investigated in terms of swelling behavior and hemo/biocompatibility. The produced hydrogels had an uniform interconnected open porous structure with a porosity of up to 95% and pores size in the range of 83-260 μm. All obtained cryogels were elastic, mechanically stable, with a superfast swelling kinetics. In vitro hemocompatibility assay gave hemolysis ratios (HRs) lower than 0.5%, which is below the permissible limit of 5%. The in vivo tolerance tests performed by implantation of cryogel specimens into Wistar rats proved their biocompatibility.

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ABSTRACT:The reaction mechanisms of N-substituted maleamic acids (MA) cyclodehydration (CDH) to the corresponding maleimides (M) and isomaleimides (IM) and IM rearrangement to M were studied by the PM3 Hamiltonian with charge model 1 (CM1P) of the AMSOL computational method with solvation effect in order to establish the most probable pathways. CDH was considered in the presence of acetic anhydride in the presence of an acetate anion or triethylamine as the dehydrating agent in CH 2 Cl 2 as the solvent. In the first step, our computational results supported carboxylic proton losses, provided by a nucleophilic center on the dehydrating agent. In the next step, maleamic acid anion could either add a molecule of a dehydrating agent (path A) or cyclicize (path B). Our results indicate the path B to require more energy than path A, so path B is considered less likely to occur. The formation (path A) of an anion complex I2 between the anion of MA and the dehydration agent was supported as well as acetate anion loss to form the neutral mixed anhydride I3. The ring closure to M or IM occurs only after I3 amide proton loss, meaning that the dehydrating agent necessitate another nucleophilic center. The cyclization of I4 anion over amide nitrogen or oxygen to the reaction outcome depends on the electronic effect of amide nitrogen substituent. The same results were obtained studying CDH of N-substituted ophthalmic acids with acetic anhydride and for MA with N,NЈ-dicyclohexylcarbodiimide as dehydrating agent, in the same solvent. In such circumstances, one can consider them the common features of a general CDH reaction mechanism of MA. Our computational results found the IM to M rearrangement to correspond to the reversible final path of synthesis mechanism although the other investigators considered it to take place under a different reaction. They also supported the importance of the acetate anion in both cyclization and rearrangement mechanisms; the presence of tertiary amine blocks the acetic acid formed during reaction, determines I3 amide proton loss and prevents rearrangement. The theoretical conclusions are consistent with the experimental results.