Asymmetric Synthesis of Axinellamines A and B

Abstract

Axinellamines A and B are broad-spectrum anti-bacterial pyrrole–imidazole alkaloids that have a complex polycyclic skeleton. A new asymmetric synthesis of these marine sponge metabolites is described herein, featuring an oxidative rearrangement and an anchimeric chlorination reaction.

Highly Selective Conversion of CO2 to CO Achieved by a Three‐Dimensional Porous Silver Electrocatalyst

“…[42] Despite the high catalytic activity, the AgFoam 60 electrode requires a high overpotential of 0.88 V relative to the CO 2 /CO equilibrium potential of À0.11 V vs RHE. In retrospect, anodized Ag (92 % at À0.6 V), [28] oxide-derived Ag (89.5 % at À0.8 V), [8] de-alloyed nanoporous Ag (92 % at À0.6 V) [30] and nanocoral Ag catalyst (95 % at À0.6 V) [43] display very high catalytic performance for the conversion of CO 2 to CO at lower overpotentials. Nonetheless, the AgFoam 60 electrode may be favoured for potential scaling up for large scale applications due to its facile fabrication and moderately high catalytic performance in delivering high Faradaic efficiency (94.7 %) and mass specific CO current density (2.84 A g À1 ) at an applied potential of À0.99 V ( Figure S5).…”

“…On the basis of such observation, it is understood that rate determining step for the AgFoam 60 electrode is the initial transfer of one electron to a CO 2 molecule to form the *CO 2 C À intermediate adsorbed (* represents surface adsorbed species) to the surface. [8,30,41] Therefore, it is conjectured that the high performance of the AgFoam 60 electrode for CO 2 RR is due to the greater stabilization of the rate determining *CO 2 C À radical intermediate on the active sites present in the high index facets that is present in the highly porous three dimensional electrode compared to Ag foil. Similar conclusion was also reported with the nanoporous Ag catalyst where the high catalytic performance was attributed to the greater active sites present in the high index faceted curved catalyst.…”

“…[3,4] If coupled with electricity generated from renewable energy resources such as wind and solar, electrochemical reduction of CO 2 will provide additional benefits of storing the diffusive and intermittent renewable energy resources in the form of chemical fuels, which facilitates their storage, distribution and fulfils the purpose of continuous usage. [5][6][7] However, the major hurdle lies within a widespread application of electrochemical CO 2 reduction reactions (CO 2 RR) is its sluggish reaction kinetics, which requires a substantial amount of overpotential (for example Ag foil requires overpotential > 0.9 V) [8] to generate value added chemical feedstocks at acceptable rates that render this process very energy inefficient. [9,10] As a result, highly efficient and stable catalysts are urgently required for advocating the commercialization of the CO 2 RR process.…”

Hollow CuS Microcube Electrocatalysts for CO2 Reduction Reaction

“…The h-CuS MCs exhibits a Tafel slope of 124 mV dec À1 , which is close to the theoretical calculated value, [38] indicating that the initial electron transfer for CO 2 activation is the rate-determining step for the overall electrocatalytic process. [31] Additionally, Figure 5c shows that the Tafel slope of h-CuS MCs increased at higher potential, which indicated that CO 2 reduction is limited by mass transport at the overpotential above 0.4 V (vs. RHE). Therefore, at a higher overpotential, the h-CuS MCs may have a stronger surface binding to *H and a rather lower concentration *CO 2 * À intermediates, which make the formation of H-H bond becomes a dominant pathway in a higher overpotential.…”

“…The large overpotential required for the CO 2 RR can be attributed to the barrier of the initial electron transfer to a CO 2 molecule. [30][31][32][33][34] Herein, we reported a hydrothermal method for the synthesis of Cu 2 O microcubes (Cu 2 O MCs), which then converted into hollow CuS microcubes (h-CuS MCs) by ionic exchange reaction. The as-prepared h-CuS MCs, benefitting from its unique structure and enhanced exposed edge sites, show a significantly improved electrocatalytic activities and selectively toward electrocatalytic reduction conversion of CO 2 to CO.…”