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Molecular force probes that generate optical responses to critical levels of mechanical stress (mechanochromophores) are increasingly attractive tools for identifying molecular sites that are most prone to failure. Here, a coumarin dimer mechanophore whose mechanical strength is comparable to that of the sulfur–sulfur bonds found in vulcanized rubbers is reported. It is further shown that the strain‐induced scission of the coumarin dimer within the matrix of a particle‐reinforced polybutadiene‐based co‐polymer can be detected and quantified by fluorescence spectroscopy, when cylinders of the nanocomposite are subjected to unconstrained uniaxial stress. The extent of the scission suggests that the coumarin dimers are molecular "weak links" within the matrix, and, by analogy, sulfur bridges are likely to be the same in vulcanized rubbers. The mechanophore is embedded in polymer main chains, grafting agent, and cross‐linker positions in a polymer composite in order to generate experimental data to understand how macroscopic mechanical stress is transferred at the molecular scale especially in highly entangled cross‐linked polymer nanocomposite. Finally, the extent of activation is enhanced by approximately an order of magnitude by changing the regiochemistry and stereochemistry of the coumarin dimer and embedding the mechanophore at the heterointerface of the particle‐reinforced elastomer. [ABSTRACT FROM AUTHOR]

Enantioselective synthesis of the piperidine alkaloids, (-)-adaline (1) and (-)-euphococcinine (2), were achieved from 7 in a six-step sequence through stepwise allylic transfer reactions. Dramatic additive effect of Bu3SnF for the conversion of 3 into 9 was observed to expedite the process to afford the cyclized products in good yields. [ABSTRACT FROM AUTHOR]

Topological molecular connections and structures, including physical entanglements in polymer networks, knots along polymer chains, and rotaxanes in sliding ring gels, have important consequences for the physical properties of polymeric materials. Often these topologies contribute through their ability to bear mechanical stress, but experimental measures of their relative mechanical strength are rare. Here, we use sonochemical polymer mechanochemistry to assess the relative mechanical strength of a multicatenane copolymer relative to copolymers of cyclic and linear analogs. The relative mechanical strengths are obtained by comparing the limiting molecular weights (M lim ) and contour lengths (L lim ) of the polymers under pulsed ultrasound of their dilute solutions. The values of M lim and L lim , and thus the inferred mechanical strengths of the polymers, are effectively identical. The mechanical bonds of the catenanes are therefore as strong, or stronger, mechanically as the covalent bonds along the polymer backbone., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)