1,5-Asymmetric induction during nucleophilic additions to arene­tricarbonyl­chromium complexes: tri­carbonyl­(η6-1-methyl-4-{spiro­[(1R,2S)-1,7,7-trimethyl­bicyclo­[2.2.1]heptane-3,2′-1,3-dioxolan]-2-yl­oxy}benzene)­chromium

The tricarbonyl­chromium unit bound to the arene ring of the chiral title complex, [Cr(C19H26O3)(CO)3], is rotated by ca 25° in agreement with the proposed mechanism for 1,5-asymmetric induction of nucleophilic attack

Progress Toward the Total Synthesis of Formicamycin H

The type II polyketide formicamycin H is a complex pentacyclic molecule possessing a tetracyclic core and an element of axial chirality. Our synthetic strategy highlights a recently developed [4+2] cycloaddition developed by the Krische laboratory for a convergent synthesis of the natural product, which, to date, has no previously reported synthesis. Our progress toward formicamycin H is described.Chemistr

Metal-Mediated Vinylogous Nazarov Cyclization Reaction

The Nazarov cyclization reaction has been used as an effective method to synthesize cyclopentanones. While 6-membered ring systems can be available by way of the homo Nazarov variant, 7-membered ring formation involving a Nazarov-type reaction is very rare, and completely unknown thermally. Using the established concept of the ability of the alkyne-Co2(CO)6 moiety to enable the formation of -carbonyl cations and the good stability of this generated cation, 7-membered ring formation via the vinylogous Nazarov reaction with electron deficient enones has been investigated. The desired aryl substituted enyone-Co2(CO)6 complex precursors for the cyclization reaction have been prepared from commercially available starting materials, using a series of reactions that include Sonogashira cross-coupling, desilylation, organolithium reactions with aldehydes, oxidation and complexation reactions. The treatment of the respective complex precursors, using SnCl4 as a suitable Lewis acid, successfully generated cycloheptynone-Co2(CO)6 complexes. The substitution effects have been examined, showing that introducing a bulky group at the alpha-position to the carbonyl enhances the cyclization efficiency by enabling the desired s-trans/s-trans conformation. On the other hand, beta-substituting with an R group other than H atom reduces the reaction rate and allows formation of the desired 7-membered ring only in very low yield. Preparation of appropriate dienynone-Co2(CO)6 complex substrates allowed expansion of the reaction scope to non-aromatic starting materials. Successful reductive decomplexation of the cycloheptynone-Co2(CO)6 unit also was demonstrated

Reactions of Trimethylaluminium: Modelling the Chemical Degradation of Synthetic Lubricants

In investigating and seeking to mimic the reactivity of trimethylaluminium (TMA) with synthetic, ester-based lubricating oils, the reaction of methyl propionate $\textbf{1}$ was explored with 1, 2 and 3 equivalents of the organoaluminium reagent. Spectroscopic analysis points to the formation of the adduct $\textbf{1}$ (TMA) accompanied only by the low level 1:1 production of Me$_{2}$AlOCEtMe$_{2}$ $\textbf{2}$ and Me$_{2}$AlOMe $\textbf{3}$ when an equimolar amount of TMA is applied. The deployment of excess TMA favours reaction to give $\textbf{2}$ and $\textbf{3}$ over $\textbf{1}$(TMA) adduct formation and spectroscopy reveals that in hydrocarbon solution substitution product $\textbf{2}$ traps unreacted TMA to yield $\textbf{2}$(TMA). The $^{1}$H NMR spectroscopic observation of two Al-Me signals not attributable to free TMA and in the ratio 1:4 suggests the formation of a previously only postulated, symmetrical metallacycle in Me$_{4}$Al$_{2}$ (μ$^{2}$-Me)(μ$^{2}$-OCEtMe$_{2}$ ). In the presence of $\textbf{3}$, $\textbf{2}$(TMA) undergoes thermally induced exchange to yield Me$_{4}$Al$_{2}$(μ$^{2}$-OMe)(μ$^{2}$-OCEtMe$_{2}$) $\textbf{4}$ and TMA. The reaction of methyl phenylacetate $\textbf{5}$ with TMA allows isolation of the crystalline product Me$_{2}$AlOCBnMe$_{2}$ (TMA) $\textbf{6}$(TMA), which allows the first observation of the Me$_{}$ Al$_{2}$(μ$^{2}$-Me)(μ$^{2}$-OR) motif in the solid state. Distances of 2.133(3) Å (Al-Me$_{bridging}$) and 1.951 Å (mean Al-Me$_{terminal}$) are recorded. The abstraction of TMA from $\textbf{6}$(TMA) by the introduction of Et$_{2}$O has yielded $\textbf{6}$, which exists as a dimer.This work was supported by Cambridge Refrigeration Technology (J.S.). The U.K. EPSRC are acknowledged for grant EP/J500380/1 (A.J.P.)

Carbon monoxide (CO) cycling in the Fram Strait, Arctic Ocean

Carbon monoxide (CO) influences the radiative budget and oxidative capacity of the atmosphere over the Arctic Ocean, which is a source of atmospheric CO. Yet, oceanic CO cycling is understudied in this area, particularly in view of the ongoing rapid environmental changes. We present results from incubation experiments conducted in the Fram Strait in August/September 2019 under different environmental conditions: While lower pH did not affect CO production (GPCO) or consumption (kCO) rates, enhanced GPCO and kCO were positively correlated with coloured dissolved organic matter (CDOM) and dissolved nitrate concentrations, respectively, suggesting microbial CO uptake under oligotrophic conditions to be a driving factor for variability in CO surface concentrations. Both production and consumption of CO will likely increase in the future, but it is unknown which process will dominate. Our results will help to improve models predicting future CO concentrations and emissions and their effects on the radiative budget and the oxidative capacity of the Arctic atmosphere

Advances in understanding of air-sea exchange and cycling of greenhouse gases in the upper ocean

\ua9 2024 University of California Press. All rights reserved. The air–sea exchange and oceanic cycling of greenhouse gases (GHG), including carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), carbon monoxide (CO), and nitrogen oxides (NOx \ubc NO \ufe NO2), are fundamental in controlling the evolution of the Earth’s atmospheric chemistry and climate. Significant advances have been made over the last 10 years in understanding, instrumentation and methods, as well as deciphering the production and consumption pathways of GHG in the upper ocean (including the surface and subsurface ocean down to approximately 1000 m). The global ocean under current conditions is now well established as a major sink for CO2, a major source for N2O and a minor source for both CH4 and CO. The importance of the ocean as a sink or source of NOx is largely unknown so far. There are still considerable uncertainties about the processes and their major drivers controlling the distributions of N2O, CH4, CO, and NOx in the upper ocean. Without having a fundamental understanding of oceanic GHG production and consumption pathways, our knowledge about the effects of ongoing major oceanic changes—warming, acidification, deoxygenation, and eutrophication—on the oceanic cycling and air–sea exchange of GHG remains rudimentary at best. We suggest that only through a comprehensive, coordinated, and interdisciplinary approach that includes data collection by global observation networks as well as joint process studies can the necessary data be generated to (1) identify the relevant microbial and phytoplankton communities, (2) quantify the rates of ocean GHG production and consumption pathways, (3) comprehend their major drivers, and (4) decipher economic and cultural implications of mitigation solutions

Riding the Wave of Monodentate Ligand Revival : from the A/B Concept to Noncovalent Interactions

The rediscovery of chiral monodentate ligands made in the period 1999\u20132003 had important consequences in enantioselective transition-metal catalysis, such as the introduction of the A/B concept (i.e., use of monodentate ligand mixtures) and, later, a renewed interest in supramolecular ligands capable of ligand\u2013ligand and ligand\u2013substrate interactions. This Personal Account summarizes the contributions made by our research group in this area in the period 2004\u20132015, which reflect the abovementioned developments. Within this area, we introduced some original concepts, such as 1) the use of chiral tropos ligand mixtures; 2) the development of new strategies to maximize heterocomplex formation from combinations of simple monodentate ligands; 3) the investigation of new ligand\u2013ligand interactions to achieve selective heterocomplex formation; and 4) the development of highly efficient and synthetically accessible supramolecular ligands

Cross-dehydrogenative coupling and oxidativeamination reactions of ethers and alcohols with aromatics and heteroaromatics

Cross-dehydrogenative coupling (CDC) is a process in which, typically, a C–C bond is formed at the expense of two C–H bonds, either catalyzed by metals or other organic compounds, or via uncatalyzed processes. In this perspective, we present various modes of C–H bond-activation at sp3 centers adjacent to ether oxygen atoms, followed by C–C bond formation with aromatic systems as well as with heteroaromatic systems. C–N bond-formation with NH-containing heteroaromatics, leading to hemiaminal ethers, is also an event that can occur analogously to C–C bond formation, but at the expense of C–H and N–H bonds. A large variety of hemiaminal ether-forming reactions have recently appeared in the literature and this perspective also includes this complementary chemistry. In addition, the participation of C–H bonds in alcohols in such processes is also described. Facile access to a wide range of compounds can be attained through these processes, rendering such reactions useful for synthetic applications via Csp3 bond activations

Preparation of novel steroidal conjugates as potential diagnostic and therapeutic agents with an emphasis on quinoid and halogenated moieties

Steroids bonded to pharmaceutically active molecules are interesting candidates as therapeutic agents. In this work, a number of potentially bioactive residues, which include the quinoid moiety, have been synthesized as a simple steroid quinone hybrid, where the steroid component will be estradiol derived or the steroid cholesterol derived. For this purpose, two novel reactions have been explored namely, the modification of the APPEL reaction to connect residues by using PPh3/BrCCl3 for amidation and esterification of carboxylic acids. Another one is the hydrogenation reaction of alkenes by using NaBH4, AcOH, Pd/C and toluene or benzene in the presence of benzyl groups with hydrogen production in situ. The halogenation of residues that can be linked to steroids has also been attempted. The main aim of the proposal work is the development of a strategy that can be adopted for the radio-halogenation of the residues that function as potential radiodiagnostic agents when linked to the steroid