An efficient synthesis of pyranonaphthoquinones is achieved by ethylenediamine diacetate-catalyzed reactions of 4-hydroxy-2-quinolones with a variety of a,b-unsaturated aldehydes in moderate yields. This method provides a rapid entry into biologically interesting a-lapachone derivatives with a variety of substituents on the pyran ring.
Redundant actuation for the parallel kinematic machine (PKM) is a well-known technique for overcoming general drawbacks of the PKM by helping it to avoid singularity and enhance stiffness characteristics, among others. Torque distribution plays a critical role in redundant actuation because this actuation causes the PKM to consume too much energy or put a substantial amount of stress on joints and links. This paper proposes a new torque distribution method for reducing the maximum torque of the actuator of a planar PKM. Here the main idea behind the proposed method is the use of superposition of a particular solution for a non-redundant case and an optimized null-space solution for a redundant case with a constant coefficient. The optimal value of a null-space solution can be easily determined by checking only the intersection points of the profile of the actuator's torque as the coefficient varies. We consider three cases of planar PKMs-2-, 3-, and 4-RRR PKMs-and present a detailed procedure for deriving a kinematic solution for the 2-RRR PKM based on Screw theory. We compare the proposed method with the minimum-norm pseudo-inverse method and assess a limitation of the proposed method. The torque distribution algorithm can be used to determine the number of actuators in an efficient manner and to reduce energy consumption.
A Concise Route for the Synthesis of Pyranonaphthoquinone Derivatives. -Reaction of 4-hydroxy-2-quinolone (I) with α,β-unsaturated aldehydes, catalyzed by ethylenediamine diacetate, leads to an efficient synthesis of pyranonaphthoquinones. The method offers a short access to the biologically interesting α-lapachone (IV) and a variety of its derivatives. -(LEE*, Y. R.; CHOI, J. H.; TRINH, D. T. L.; KIM, N. W.; Synthesis 2005, 18, 3026-3034; Sch. Chem. Eng. Technol., Coll. Eng., Yeungnam Univ., Kyongsan 712-749, S. Korea; Eng.) -Mais 13-143
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.