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Z-Olefins are challenging synthetic targets owing to their relative thermodynamic instability. Transition metal–catalyzed asymmetric allylic substitution reactions are well known for installing stereocenters adjacent to branched or E-linear olefins. However, analogous reactions for the synthesis of optically active Z-olefin products are rare. Here we report iridium-catalyzed asymmetric allylic substitution reactions that retain Z-olefin geometries while establishing an adjacent quaternary stereocenter. The formation of transient anti-π-allyl-iridium intermediates and their capture by external nucleophiles before isomerization to the thermodynamically more stable syn-π-allyl-iridium counterparts have been observed. These results provide a promising method for preparing chiral Z-olefinic compounds.

To meet the demand of modern acoustic absorbing material for which acoustic absorbing frequency region can be readily tailored, we introduced woodpile structure into locally resonant phononic crystal ͑LRPC͒ and fabricated an underwater acoustic absorbing material, which is called locally resonant phononic woodpile ͑LRPW͒. Experimental results show that LRPW has a strong capability of absorbing sound in a wide frequency range. Further theoretical research revealed that LRPC units and woodpile structure in LRPW play an important role in realization of wide band underwater strong acoustic absorption.