The first total syntheses of taiwaniadducts B, C, and D have been accomplished. Two diterpenoid segments were prepared with high enantiopurity, both through Ir-catalyzed asymmetric polyene cyclization. A sterically demanding intermolecular Diels-Alder reaction promoted by Er(fod)3 assembled the scaffold of taiwaniadducts B and C. A carbonyl-ene cyclization forged the cage motif of taiwaniadduct D at a late stage, providing over 200 mg of this compound.

Oh my darling, Drimentine: The first total synthesis of the pyrroloindoline alkaloids drimentines A, F, and G, and their congener, indotertine A, is reported. An intermolecular radical conjugate addition was key in the synthesis of the drimentine alkaloids, and a biologically inspired iminium–olefin cyclization converted drimentine F into indotertine A.

Single-crystal materials with sufficiently low crystal symmetry and strong spin-orbit interactions can be used to generate novel forms of spin-orbit torques on adjacent ferromagnets, such as the out-of-plane antidamping torque previously observed in WTe 2 /ferromagnet heterostructures.Here, we present measurements of spin-orbit torques produced by the low-symmetry material β-MoTe 2 , which unlike WTe 2 retains bulk inversion symmetry. We measure spin-orbit torques on β-MoTe 2 /Permalloy heterostructures using spin-torque ferromagnetic resonance as a function of crystallographic alignment and MoTe 2 thickness down to the monolayer limit. We observe an outof-plane antidamping torque with a spin torque conductivity as strong as 1/3 of that of WTe 2 , demonstrating that the breaking of bulk inversion symmetry in the spin-generation material is not a necessary requirement for producing an out-of-plane antidamping torque. We also measure an unexpected dependence on the thickness of the β-MoTe 2 -the out-of-plane antidamping torque is present in MoTe 2 /Permalloy heterostructures when the β-MoTe 2 is a monolayer or trilayer thick, but goes to zero for devices with bilayer β-MoTe 2 .1 arXiv:1906.01068v1 [cond-mat.mes-hall] 3 Jun 2019Spin-orbit torques represent one of the most promising methods for manipulating emerging magnetic memory technologies [1]. When a charge current is applied to a material with large spin-orbit coupling, such as a heavy metal [2][3][4][5][6][7], topological insulator [8,9], or transition metal dichalcogenide (TMD) [10-16], a spin current generated through mechanisms such as the spin Hall or Rashba-Edelstein effects can be used to exert a torque on an adjacent ferromagnet. Recent work from several research groups has focused on understanding how a controlled breaking of symmetry in a spin-generating material / ferromagnet heterostructure can be used to tune the direction of the observed spin-orbit torques for optimal switching of magnetic devices [12][13][14][17][18][19][20][21][22][23][24]. For instance, the presence of magnetic order within a spin-generation layer can allow current-generated spin directions that are typically forbidden for highly-symmetric non-magnetic metals [17][18][19][20]. Similarly, our group has shown that by using WTe 2 as the spin-source material, a TMD with a low-symmetry crystal structure, it is possible to generate an out-of-plane antidamping torque [12,13] -the component of torque required for the most efficient mode of switching for magnets with perpendicular magnetic anisotropy, but forbidden in higher-symmetry materials. Only one other material, SrRuO 3 , has been shown to generate an out-of-plane antidamping spin-orbit torque [20], arising from symmetry breaking associated with magnetic order. Many questions remain regarding the mechanism and necessary conditions for generating a strong out-of-plane antidamping torque.In this work, we study the spin-orbit torques generated in TMD/ferromagnet heterostructures with a crystal symmetry that is distinct from WTe 2 i...

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Memristors, demonstrated by solid-state devices with continuously tunable resistance, [1][2][3][4][5][6][7] have emerged as a new paradigm for self-adaptive networks that require synapse-like functions (artificial synapse, for example). Spin-based memristors offer advantages over other types of memristors because of their significant endurance and high energy efficiency. [8,9] Yet, it remains a challenge to build dense and functional spintronic memristors with structures and materials that are compatible with existing ferromagnetic devices. [10] Here, a memristive device based upon Ta/CoFeB/MgO heterostructures is demonstrated, which are commonly used in out-of-plane magnetized magnetic tunnel junctions. [11] To achieve the memristive function, a domain wall (DW) is driven back and forth in a continuous manner in the CoFeB layer by applying in-plane positive or negative current pulses along the Ta layer, utilizing the spin-orbit torque (SOT) that the current exerts on the CoFeB magnetization. [12][13][14][15][16][17] Hence, Memristors, demonstrated by solid-state devices with continuously tunable resistance, have emerged as a new paradigm for self-adaptive networks that require synapse-like functions (artificial synapse, for example). Spin-based memristors offer advantages over other types of memristors because of their significant endurance and high energy efficiency. Yet it remains a challenge to build dense and functional spintronic memristors with structures and materials that are compatible with existing ferromagnetic devices. Here, a memristive device based upon Ta/CoFeB/MgO heterostructures is demonstrated, which are commonly used in out-of-plane magnetized magnetic tunnel junctions (MTJ). To achieve the memristive function, a domain wall (DW) is driven back and forth in a continuous manner in the CoFeB layer by applying in-plane positive or negative current pulses along the Ta layer, utilizing the spin-orbit torque (SOT) that the current exerts on the CoFeB magnetization. Hence, the magnetization and consequently the anomalous Hall effect (AHE) resistance are modulated in an analog manner, being controlled by the pulsed current characteristics including amplitude, duration, and repetition number. The quasi-continuous AHE resistance variation is explained by the SOT-induced DW creep motion. These results pave the way for developing SOT-based energy-efficient neuromorphic systems.

A divergent approach was developed toward the total synthesis of taiwaniaquinoids. An advanced intermediate 5a with trans A/B ring junction was concisely assembled by employing a Bi(OTf)3-catalyzed cationic cyclization and a Wolff-type ring contraction as key steps. This common intermediate was readily converted to racemic taiwaniaquinones A and F and taiwaniaquinols B and D, respectively.

Shishijimicin A is a scarce marine natural product with highly potent cytotoxicities, making it a potential payload or a lead compound for designed antibody-drug conjugates. Herein, we describe an improved total synthesis of shishijimicin A and the design, synthesis, and biological evaluation of a series of analogues. Equipped with appropriate functionalities for linker attachment, a number of these analogues exhibited extremely potent cytotoxicities for the intended purposes. The synthetic strategies and tactics developed and employed in these studies included improved preparation of previously known and new sulfenylating reagents such as PhthNSSMe and related compounds.

Emergent quantum phenomena in electronically coupled two-dimensional heterostructures are central to nextgeneration optical, electronic, and quantum information applications. Tailoring electronic band gaps in coupled heterostructures would permit control of such phenomena and is the subject of significant research interest. Two-dimensional polymers (2DPs) offer a compelling route to tailored band structures through the selection of molecular constituents. However, despite the promise of synthetic flexibility and electronic design, fabrication of 2DPs that form electronically coupled 2D heterostructures remains an outstanding challenge. Here, we report the rational design and optimized synthesis of electronically coupled semiconducting 2DP/2D transition metal dichalcogenide van der Waals heterostructures, demonstrate direct exfoliation of the highly crystalline and oriented 2DP films down to a few nanometers, and present the first thickness-dependent study of 2DP/MoS 2 heterostructures. Control over the 2DP layers reveals enhancement of the 2DP photoluminescence by two orders of magnitude in ultrathin sheets and an unexpected thickness-dependent modulation of the ultrafast excited state dynamics in the 2DP/MoS 2 heterostructure. These results provide fundamental insight into the electronic structure of 2DPs and present a route to tune emergent quantum phenomena in 2DP hybrid van der Waals heterostructures.