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  1. Carbenes (R1R2C:) [like radicals, arynes, and nitrenes] constitute a significant family of neutral, high-energy, reactive intermediates – fleeting chemical entities that undergo rapid reactions. An alkyne (R3C≡CR4) is a fundamental functional group that houses a high degree of potential energy; however, the substantial kinetic stability of alkynes renders them conveniently handleable as shelf-stable chemical commodities. The ability to generate metal-free carbenes directly from alkynes, fueled by the high potential (that is, thermodynamic) energy of the latter, would constitute a significant advance. We report here that this can be achieved simply by warming a mixture of a 2-alkynyl-iminoheterocycle (a cyclic compound containing a nucleophilic nitrogen atom) with an electrophilic alkyne. We demonstrate considerable generality for the process: many shelf-stable alkyne electrophiles engage many classes of (2-alkynyl)heterocyclic nucleophiles to produce carbene intermediates that immediately undergo many types of transformations to provide facile and practical access to a diverse array of heterocyclic products. Key mechanistic aspects of the reactions are delineated. 
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    Free, publicly-accessible full text available June 25, 2025
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  5. We report here a study that has revealed two distinct modes of reactivity of azobenzene derivatives (ArNNAr) with benzynes, depending on whether the aryne reacts with a trans - or a cis -azobenzene geometric isomer. Under thermal conditions, trans -azobenzenes engage benzyne via an initial [2 + 2] trapping event, a process analogous to known reactions of benzynes with diarylimines (ArCNAr). This is followed by an electrocyclic ring opening/closing sequence to furnish dihydrophenazine derivatives, subjects of contemporary interest in other fields ( e.g. , electronic and photonic materials). In contrast, when the benzyne is attacked by a cis -azobenzene, formation of aminocarbazole derivatives occurs via an alternative, net (3 + 2) pathway. We have explored these complementary orthogonal processes both experimentally and computationally. 
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  6. The purpose of this study was to learn if a convenient 1H NMR method could be developed to serve as a tool for estimating the propensity of a given lactone to participate in ring-opening transesterification polymerization (ROTEP). The methanolysis of each of 18 lactones was initially examined in CD3OD solution in the presence of sulfuric acid as a Brønsted catalyst at ambient temperature. Once equilibrium was established, the ratio of remaining lactone to the ring-opened methyl ester/alcohol could be readily measured by NMR spectroscopy. The observed thermodynamic driving force observed for the methanol ring openings is roughly in line with the extent of ROTEP for the various classes of lactones. This is the case even though the reaction conditions for these methanolyses versus ROTEP reactions are substantially different. Qualitative evaluations of the rates of the ring-opening methanolyses were also performed, and several non-obvious relative reactivities were observed. Finally, employing this simple NMR methanolysis using low concentrations of methanol in CDCl3 is recommended as the preferred protocol for the initial evaluation of the polymerizability of any new lactone monomer that researchers may prepare in the future. 
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  7. Abstract

    Arynes are fleeting, high‐energy intermediates that undergo myriad trapping reactions by nucleophiles. Their unusual reactivity compared to other electrophiles can spur unexpected mechanistic pathways enroute to the formation of benzenoid products. Herein we explore a particularly unique case of thermally generated arynes reacting with phosphoranes to form helical dibenzothiophenes and ‐selenophenes. Multiple new helical polycyclic aromatic products are reported. DP4+ and X‐ray crystallographic analysis were used in tandem to confirm the structural topologies of selected products and to demonstrate the utility of DP4+ for distinguishing between isomeric polycyclic aromatic compounds. Lastly, we discuss a plausible mechanism consistent with DFT computations that accounts for the product formation; namely, ligand coupling (i.e., reductive elimination) within a hypervalent, pentacarbon‐ligated σ‐phosphorane furnishes the dibenzothio‐ or dibenzoselenophene.

     
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  8. Abstract

    Arynes are fleeting, high‐energy intermediates that undergo myriad trapping reactions by nucleophiles. Their unusual reactivity compared to other electrophiles can spur unexpected mechanistic pathways enroute to the formation of benzenoid products. Herein we explore a particularly unique case of thermally generated arynes reacting with phosphoranes to form helical dibenzothiophenes and ‐selenophenes. Multiple new helical polycyclic aromatic products are reported. DP4+ and X‐ray crystallographic analysis were used in tandem to confirm the structural topologies of selected products and to demonstrate the utility of DP4+ for distinguishing between isomeric polycyclic aromatic compounds. Lastly, we discuss a plausible mechanism consistent with DFT computations that accounts for the product formation; namely, ligand coupling (i.e., reductive elimination) within a hypervalent, pentacarbon‐ligated σ‐phosphorane furnishes the dibenzothio‐ or dibenzoselenophene.

     
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  9. Abstract: Here we provide examples that demonstrate the value of using properly designed and easily performed doping experiments to give insights about the nature of the analyte(s) present in a 1H NMR sample. Two mixtures, the first quite complex and the second far less so, have been chosen: (i) the crude pyrolysate from reaction of butyric acid in (supercritical) water at 600 °C and (ii) a mixture of two basic amines. In the former, 13 distinct carbonyl-containing compounds, ranging in relative concentration of nearly 2 orders of magnitude, were positively identified. The latter highlights the advantage of using a doping experiment as opposed to merely comparing the spectra from two separate samples containing the same analyte. 
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