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ABSTRACT:The mechanical properties of crosslinked polymers depend on their structural features, one of which is the functionality of the crosslinks in a polymer network. To study the effect of crosslink functionality (U) on the mechanical properties of 1,2,3-triazole polymers for potential application as rocket propellant binders, crosslinkers with different U's (3, 4, 6, 16, 32, and 64) were used in the polymerization. As the percentage of acetylenic groups provided by crosslinker was kept constant and the functionality of the crosslinker increased, the resulting polymer showed a higher modulus but a lower strain. Compared to traditional polyurethane binders, 1,2,3-triazole polymers showed comparable mechanical properties, although the stress and modulus tended to be lower and the strain capability tended to be greater for the triazole-linked rubbers.

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Um rearranjo de Curtius, utilizando adutos de Morita-Baylis-Hillman como substrato, foi realizado em uma sequência que permitiu a síntese de várias hidroxi-cetonas (aciloínas) com uma grande diversidade estrutural e com bons rendimentos globais. Por sua vez, essas aciloínas foram transformadas em 1,2-amino-alcoóis de configuração relativa anti, através de uma etapa de aminação redutiva altamente diastereosseletiva. A utilidade sintética dessas abordagens foi demonstrada através das sínteses totais da (±)-bupropiona, fármaco utilizado no tratamento na síndrome de abstinência de fumantes e da (±)-espisulosina, um potente agente anti-tumoral isolado inicialmente de uma fonte marinha.Using Morita-Baylis-Hillman adducts as substrates, the Curtius rearrangement was performed in a sequence that allowed the synthesis of several hydroxy-ketones (acyloins) with great structural diversity and in good overall yields. These acyloins in turn were easily transformed into 1,2-anti aminoalcohols through a highly diastereoselective reductive amination step. The synthetic utility of these approaches was exemplified by performing the syntheses of (±)-bupropion, a drug used to treat the abstinence syndrome of smoker and (±)-spisulosine, a potent anti-tumoral compound originally isolated from a marine source. Keywords:Curtius rearrangement, Morita-Baylis-Hillman, drugs, aminoalcohols, acyloins IntroductionThe formation of new C-N bonds by incorporation of a nitrogen atom into a molecule is a fundamental transformation in organic chemistry, since it allows accessing many valuable compounds. 1 Basically, this can be achieved by nucleophilic substitution reactions or by electrophilic amination reactions. 2 A C-N bond can also be built through rearrangement reactions. For instance, Lossen, 3 Beckman, 4 Schmidt 5 and Curtius 6 rearrangements are processes which allow the efficient formation of a new C-N bond from carbonyl containing derivative compounds.The Curtius rearrangement is a thermal decomposition of a carbonyl azide leading to an isocyanate. This stereospecific rearrangement provides carbamates or amines in good overall yields and selectivities. Unfortunately, this rearrangement has the drawback that low molar mass acyl azides present an explosion hazard. 7 This safety issue has limited the industrial use of this transformation until recently, when Am Ende et al. 8 reported a new experimental protocol, which enabled the use of this reaction under safer conditions even when conducted on a large scale. This and other protocols have revived interest in this rearrangement, particularly for industrial purposes. 9 Regarding the potential of this rearrangement, our group has recently reported the preparation of some carbamates from Morita-Baylis-Hillman (MBH) adducts. 10 Curtius rearrangement would be the best way to achieve our target, since the carboxyl group in this structure is needed to perform this rearrangement. Thus, when an acid derived from a MBH adduct was treated with sodium azide, heated at reflux and treated subsequently w...