Search

Reaction experiments have confirmed that phlogopite websterite can be formed by the interaction of peridotite with hydrous alkaline- or silica-rich melts. Phlogopite websterites commonly occur as xenoliths in orogenic and intraplate volcanism but do not receive much attention. We have experimentally investigated the melting behaviour of a phlogopite websterite at 1.5 GPa (1050–1300 °C), 3.0 GPa (1100–1500 °C), and 4.5 GPa (1200–1500 °C) to contribute to understanding the sources of ultrapotassic rocks that occur in different settings. The solidus temperature of the investigated phlogopite websterite rises with increasing pressure, bracketed between 1050 and 1100 °C at 1.5 GPa, 1100 and 1150 °C at 3.0 GPa, and between 1200 and 1250 °C at 4.5 GPa. At 1.5 GPa, phlogopite websterite melts incongruently to form olivine and melt, whereas orthopyroxene, garnet, and melt are formed at 3.0 and 4.5 GPa. The transition of orthopyroxene from reactant to product with increasing pressure results in changes in the SiO2 content of melts. The experimental melts reach a maximum K2O content when phlogopite is consumed completely at temperatures ~150 °C above the solidus. The melting reactions are similar to those of phlogopite lherzolite, but the low Al2O3 starting materials result in lower Al2O3 in the melt than in melts of phlogopite lherzolite. Comparison with natural ultrapotassic rock compositions reveals that the sources of ultrapotassic rocks in convergent settings may be dominated by phlogopite websterite, phlogopite lherzolite, and phlogopite harzburgite. Sources of ultrapotassic rocks in intraplate settings are more likely to include phlogopite clinopyroxenite ± CO2 and K-richterite. In all melting experiments on phlogopite-bearing rocks, K2O from phlogopite passes into the melt, and hence the highest K2O contents in ultrapotassic rocks must be an indication of the minimum stoichiometric coefficient of phlogopite in the melting reaction. In cases where phlogopite websterite or phlogopite lherzolite is identified as the source, the minimum modal percentage of phlogopite in the source can be inferred from the highest K2O content. When applied to the Milk River minettes and New South Wales leucitites, the estimated modal proportion of phlogopite in the sources is greater than 20 wt %. Phlogopite can survive the subduction process and melt later in the post-collisional environment, whereas thermal perturbations are necessary to trigger the melting of phlogopite-bearing assemblages at the base of the lithosphere in intraplate settings. [ABSTRACT FROM AUTHOR]

The immense Tibetan Plateau is a masterpiece of the ongoing India–Asia collision. The timing of the collision is a critical parameter to reconstruct the plateau evolution, but has been not well understood yet. Here, we report a newly discovered Eocene (53.8 Ma) shoshonitic intrusion with the input of Indian continental material in the Yangbajing area of the Lhasa Terrane, south Tibet. The reverse 207Pb/206Pb zoning exhibited by feldspars, the linear isotopic arrays between whole‐rock 187Os/188Os and 1/188Os, the in‐situ feldspar 208Pb/204Pb and 206Pb/204Pb values, and the in‐situ zircon εHf(t) values and δ18O values strongly demonstrate a binary interaction process for the generation of the Yangbajing shoshonitic intrusion. Our Os isotopes further illustrate that the interaction process was dominated by recycled crustal melt assimilating minor mantle melt. In addition, different isotopic systems consistently point to an end‐member represented by the underthrust crust slice of Indian continent, which indicates that the Indian lithosphere must have already subducted beneath the Lhasa Terrane at 53.8 Ma. This is also supported by the abrupt isotopic shift toward the enriched values and the composition variation toward the high potassium contents in the subsequent Tibetan magmatism, corresponding to an increasing involvement of the Indian continental crust into the upper plate magmatism. Therefore, the Yangbajing shoshonitic intrusion is one of the earliest known magmatic evidence for the onset of the India–Asia collision. Plain Language Summary: The timing of the ongoing India–Asia collision is a critical parameter to reconstruct the plateau evolution. Here, we report a newly discovered Eocene shoshonitic intrusion with the input of Indian continental material in the Yangbajing area of the Lhasa Terrane, south Tibet. The reverse 207Pb/206Pb zoning exhibited by feldspars, the linear isotopic arrays between whole‐rock 187Os/188Os and 1/188Os, the in‐situ feldspar 208Pb/204Pb and 206Pb/204Pb values, and the in‐situ zircon εHf(t) values and δ18O values strongly demonstrate a binary interaction process for the generation of the Yangbajing shoshonitic intrusion. Our Os isotopes further illustrate that the interaction process was dominated by recycled crustal melt assimilating minor mantle melt. In addition, different isotopic systems consistently point to an end‐member represented by the underthrust crust slice of Indian continent, which indicates that the Indian lithosphere must have already subducted beneath the Lhasa Terrane at 53.8 Ma. Key Points: The early Eocene Yangbajing intrusion in the Lhasa Terrane was generated at 53.8 MaThe intrusion has recorded the subducted front of Indian Plate beneath Tibetan Plateau in the early EoceneThe onset of the India–Asia collision was prior to 53.8 Ma [ABSTRACT FROM AUTHOR]

Enantiopure TpMo(CO)(Sub 2)(pyridinyl) complexes are prepared using a scalable enzymatic kinetic resolution of the precursor to the molybdenum complex. It can function as a chiral scaffold for the enantiocontrolled synthesis of either 2,3,6-cis- or 2,6-cis-3- trans-trisubstituted piperidines.

Reports on first-principles calculations to assign a chemical identity to the variety of forms of molecular oxygen that exists on a titanium dioxide surface. Stability of geometries and spin configurations of oxygen in the bridging oxygen defect site; Role of molecular oxygen in photodegradation reactions.

Formation of andesitic rocks is crucial to understand the evolution of continental crust. Here we present an integrated study for the Paleocene Dianzhong Formation of the Linzizong volcanic succession (LVS) in the Lhasa terrane, southern Tibet. The andesites of the Dianzhong Formation have relatively high Mg# (38–60) and exhibit typical subduction‐like geochemical signatures. They are characterized by slightly enriched εNd(t) values (−2.82–0.35) and have a range of δ98/95 Mo isotopic compositions (−0.40 to 0.13 ‰) larger than mid‐ocean ridge basalt. Their high Mg#, moderate light rare earth element‐enriched patterns, and slightly enriched εNd(t) values clearly rule out an origin of continental crust‐derived melts or partial melts of earlier underplated mafic rocks. The dacites show similar geochemistry to the andesites, indicating an origin from the parental magmas of the andesites. Based on the geochemical comparisons between the Dianzhong andesites and rocks of mélange, we suggest that the andesitic rocks of the LVS were derived from partial melts of a mantle source dominated by mélange that formed along the subduction channel. The mélange diapir melting was triggered by asthenospheric upwelling and corner flow during the Paleocene slab roll‐back of northward subducted Neotethyan oceanic crust. Because the Early Paleocene andesitic rocks in southern Lhasa show an average composition of continental crust, the partial melting of mélange rocks most likely provide an important mechanism for the production of andesitic magmas within continental arcs. Key Points: The Dianzhong andesites of the LVS were generated by partial melting of mélange rocksThe Mo isotopic data support an input of subducted sediments into the magma sourceThe mélange diapir melting was triggered by the roll‐back of northward subducted Neotethyan [ABSTRACT FROM AUTHOR]

The synthesis, isolation and characterization of an activated form of the catalyst of allylic amination and etherification processes are described. An unusual mode of catalyst activation is revealed, and the finding underscores the value of delineating stoichiometric reactivity of potential catalytic intermediates.

Enantiomerically pure iron and molybdenum pi-complexes are powerful scaffolds for the enantiocontrolled construction of substituted carbo- and heterocycles. A novel and enantiocontrolled synthesis of 2,6-disubstituted piperidines using a diastereoselective methoxide abstraction of dimethoxy complexes with chiral protecting groups is disclosed.

A highly convergent large scale synthesis of a 15-membered macrocyclic hepatitis C virus (HCV) protease inhibitor BI 201302 was achieved, in which the key features are the practical macrocyclization by Ru-catalyzed ring-closing metathesis (0.1 mol % Grela catalyst, 0.1–0.2 M concentration) and the efficient sulfone-mediated SNAr reaction. [ABSTRACT FROM AUTHOR]

Velagliflozin is the active ingredient of the first oral liquid medication approved by the Food and Drug Administration for the treatment of diabetes in cats. This compound belongs to the known class of sodium-glucose cotransporter 2 inhibitors approved to treat diabetes in human. Here, we report the detailed synthesis of velagliflozin labeled with carbon 14 and carbon 13., (© 2024 John Wiley & Sons Ltd.)

We report our discovery of a novel series of potent and selective dipeptidyl peptidase IV (DPP-4) inhibitors. Starting from a lead identified by scaffold-hopping approach, our discovery and development efforts were focused on exploring structure-activity relationships, optimizing pharmacokinetic profile, improving in vitro and in vivo efficacy, and evaluating safety profile. The selected candidate, Imigliptin, is now undergoing clinical trial.

The key Pd-catalyzed cross-coupling of aryl bromides or triflates and cyclopropylmagnesium bromide in the presence of substoichiometric amounts of zinc bromide produces cyclopropyl arenes in good to excellent yields. The cross-coupling of other alkyl, cycloalkyl, and aryl Grignard reagents with aryl bromides under the same conditions gives the corresponding substituted arenes in good yields.

We report here that dramatic improvement of the key RCM reaction in the synthesis of HCV protease inhibitor BILN2061 can be achieved by N-substitution of the diene substrate with an electron-withdrawing group. Mechanistic studies using 1H NMR spectroscopy showed an unprecedented switch of the initiation sites and the correlation between such switch and the results of RCM, from the unmodified to the modified substrates. We also provided theoretical evidence that such modification may also increase the thermodynamic preference of the macrocyclic product over the diene substrate.

[reaction: see text] The yields, enantioselectivities, and regioselectivities of the reactions of amines and phenoxides with allylic carbonates in the presence of a metallacyclic iridium catalyst were compared. These data show that both preactivation of the catalyst and the size of the ligand affect the yield, enantioselectivity, and regioselectivity. With the activated catalyst containing a bis-naphthethylamino group, the allylic amination and etherification of a broad range of allylic carbonates occurred in high yields and with high regioselectivities and enantioselectivities.