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The configuration assignment at the carbohydrate anomeric carbon is a problem in the synthesis of C-glycosides. To address this, a study on the detailed analysis of 1H and 13C nuclear magnetic resonance spectrometry of pyranosyl and furanosyl C-glycosides is presented. This included the examination of 1H-1H coupling constants, 1H chemical shifts, 13C chemical shifts, 1H-13C coupling constants and nuclear Overhauser effects during irradiation of H1', H4', and H5'. This procedure enables unambiguous assignment of a C-glycoside to alpha or beta anomer series without anomer comparison.

A study was conducted to characterize an approach to heterocycle using a popolohuanone E model system. Spectroscopic analyses were carried out to determine the identities of singular materials while an intramolecular 5-exo-trig cyclization supported a hemiketal. Results indicated that the inclusion of an external reducing agent could decouple the establishment of intermolecular dimers from intramolecular systems.

A new study provides detailed chemical computations and recommended rate coefficients for the reaction of nitrous oxide with O atoms.

A new study uses the high-temperature photochemistry technique to measure rate coefficients for the consumption of O atoms by their reaction with nitrous oxide at intermediate temperatures.

Water addition to Sm(II) has been shown to increase reactivity for both SmI 2 and SmBr 2 . Previous work in our groups has demonstrated that this increase in reactivity can be attributed to coordination induced bond weakening enabling substrate reduction through proton-coupled electron transfer. The present work examines the interaction of water with samarium dichloride (SmCl 2 ) and illustrates the importance of the Sm-X interaction and bond distance upon water addition critical for the reactivity of the reagent system. Born-Oppenheimer molecular dynamics simulations identify substantial variations among the reductants created in solution upon water addition to SmI 2 , SmBr 2 , and SmCl 2 with the latter showing the least halide dissociation. This results in a lower water coordination number for SmCl 2 , creating a more powerful reducing system. As previously shown with the other SmX 2 -water systems, coordination-induced bond-weakening of the O-H bond of water bound to Sm(II) results in significant bond weakening. In the case of SmCl 2 , the bond weakening is estimated to be in the range of 83 to 88.5 kcal/mol.

The addition of water to samarium(II) has been demonstrated to have a significant impact on the reduction of organic substrates, with the majority of research dedicated to the most widely used reagent, samarium diiodide (SmI 2 ). The work presented herein focuses on the reducing capabilities of samarium dibromide (SmBr 2 ) and demonstrates how the modest change in halide ligand results in observable mechanistic differences between the SmBr 2 -water and the SmI 2 -water systems that have considerable implications in terms of reactivity between the two reagents. Quantum chemical results from Born-Oppenheimer molecular dynamics simulations show significant differences between SmI 2 -water and SmBr 2 -water, with the latter displaying less dissociation of the halide, which results in a lower coordination number for water. Experimental results are consistent with computational results and demonstrate that the coordination sphere of SmBr 2 is saturated at lower concentrations of water. In addition, coordination-induced bond-weakening of the O-H bond is demonstrably different for water bound to SmBr 2 , leading to an estimated O-H bond-weakening of at least 83 kcal/mol, nearly 10 kcal/mol larger than the bond-weakening observed in SmI 2 -H 2 O. Experimental results also demonstrate that the use of alcohols in place of water with SmBr 2 leads to substrate reduction, albeit several orders of magnitude slower than for SmBr 2 -water. The difference in rates resulting from the change in proton donor is attributed to a rate-limiting proton-coupled electron transfer in SmBr 2 -water and a sequential electron transfer then proton transfer in SmBr 2 -alcohol systems, where electron transfer is rate-limiting.

The reduction of a carbonyl by SmI 2 -water is the first step in a range of reactions of synthetic importance. Although the reduction is often proposed to proceed through an initial stepwise electron-transfer-proton-transfer (ET-PT), recent work has shown that carbonyls and related functional groups are likely reduced though proton-coupled electron-transfer (PCET). In the present work, the reduction of an activated ester, aldehyde, a linear and cyclic ketone, and related sterically demanding carbonyls by SmI 2 -H 2 O was examined through a series of mechanistic experiments. Kinetic studies demonstrate that all substrates exhibit significant increases in the rate of reduction by SmI 2 as [H 2 O] is increased. Under identical conditions, ketones and an aldehyde containing a methyl adjacent to the carbonyl are reduced slower than an unsubstituted variant by an order of magnitude, demonstrating the importance of substrate coordination. In the case of unactivated substrates, rates of reduction show excellent correlation with the calculated bond dissociation free energy of the O-H bond of the intermediate ketyl and the calculated free energy of intermediate ketyl radical anions derived from unhindered substrates: findings consistent with concerted PCET. Activated esters derived from methylbenzoate are likely reduced through stepwise or asynchronous PCET. Overall, this work demonstrates that the combination of the coordination of substrate and water to Sm(II) provides a configuration uniquely suited to a coupled electron- and proton-transfer process.

Reduction of carbonyls by SmI2 is significantly impacted by the presence of water, but the fundamental step(s) of initial transfer of a formal hydrogen atom from the SmI2-water reagent system to produce an intermediate radical is not fully understood. In this work, we provide evidence consistent with the reduction of carbonyls by SmI2-water proceeding through proton-coupled electron transfer (PCET). Combined rate and computational studies show that a model aldehyde and ketone are likely reduced through an asynchronous PCET, whereas reduction of a representative lactone occurs through a concerted PCET. In the latter case, concerted PCET is likely a consequence of significantly endergonic initial electron transfer.