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1. Asymmetric [4 + 2], [6 + 2], and [6 + 4] Cycloadditions of Isomeric Formyl Cycloheptatrienes Catalyzed by a Chiral Diamine Catalyst

   https://doi.org/10.1021/jacs.3c09551  

   Kaasik, Mikk; Chen, Pan-Pan; Ričko, Sebastijan; Jørgensen, Karl Anker; Houk, K. N. (November 2023, Journal of the American Chemical Society)
2. Ambimodal Bispericyclic [6 + 4]/[4 + 6] Transition State Competes with Diradical Pathways in the Cycloheptatriene Dimerization: Dynamics and Experimental Characterization of Thermal Dimers

   https://doi.org/10.1021/jacs.2c10407  

   Zhou, Qingyang; Thøgersen, Mathias K.; Rezayee, Nomaan M.; Jørgensen, Karl Anker; Houk, K. N. (December 2022, Journal of the American Chemical Society)
3. Huisgen's 1,3‐Dipolar Cycloadditions to Fulvenes Proceed via Ambimodal [6+4]/[4+2] Transition States

   https://doi.org/10.1002/anie.202005265  

   Liu, Fang; Chen, Yu; Houk, K. N. (June 2020, Angewandte Chemie International Edition)

   Abstract Huisgen's 1960 announcement of the concept of 1,3‐dipolar cycloadditions was published the year before Alder's study of the reaction of diazomethane and dimethylfulvene. The diazomethane reaction was studied again in 1970 by Houk et al. and shown to give a [6+4] adduct. Padwa's nitrile ylide cycloaddition to dimethylfulvene (1978) gave [6+4] and [4+2] adducts. We performed computational studies of these reactions with density functional theory (DFT) and show that they involve ambimodal [6+4]/[4+2] transition states that can lead to either type of cycloadduct from one transition state. We dedicate this paper to the extraordinary life and humanity of Rolf Huisgen, and to the undying influence of his discoveries on chemistry. 

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4. Catalytic Enantioselective Hetero-[6+4] and -[6+2] Cycloadditions for the Construction of Condensed Polycyclic Pyrroles, Imidazoles, and Pyrazoles

   https://doi.org/10.1021/jacs.8b13659  

   Bertuzzi, Giulio; Thøgersen, Mathias Kirk; Giardinetti, Maxime; Vidal-Albalat, Andreu; Simon, Adam; Houk, K. N.; Jørgensen, Karl Anker (February 2019, Journal of the American Chemical Society)
5. Experimental and computational phase boundary mapping of Co ₄ Sn ₆ Te ₆

   https://doi.org/10.1039/c8ta07539e  

   Crawford, Caitlin M.; Ortiz, Brenden R.; Gorai, Prashun; Stevanovic, Vladan; Toberer, Eric S. (December 2018, Journal of Materials Chemistry A)

   Binary Co 4 Sb 12 skutterudite (also known as CoSb 3 ) has been extensively studied; however, its mixed-anion counterparts remain largely unexplored in terms of their phase stability and thermoelectric properties. In the search for complex anionic analogs of the binary skutterudite, we begin by investigating the Co 4 Sb 12 –Co 4 Sn 6 Te 6 pseudo-binary phase diagram. We observe no quaternary skutterudite phases and as such, focus our investigations on the ternary Co 4 Sn 6 Te 6 via experimental phase boundary mapping, transport measurements, and first-principles calculations. Phase boundary mapping using traditional bulk syntheses reveals that the Co 4 Sn 6 Te 6 exhibits electronic properties ranging from a degenerate p-type behavior to an intrinsic behavior. Under Sn-rich conditions, Hall measurements indicate degenerate p-type carrier concentrations and high hole mobility. The acceptor defect Sn Te , and donor defects Te Sn and Co i are the predominant defects and rationally correspond to regions of high Sn, Te, and Co, respectively. Consideration of the defect energetics indicates that p-type extrinsic doping is plausible; however, Sn Te is likely a killer defect that limits n-type dopability. We find that the hole carrier concentration in Co 4 Sn 6 Te 6 can be further optimized by extrinsic p-type doping under Sn-rich growth conditions. 

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