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1. Diastereoselective Synthesis of Benzoxanthenones

   https://doi.org/10.1002/asia.201901727  

   Neuhaus, William_C; Kozlowski, Marisa_C (March 2020, Chemistry – An Asian Journal)

   Abstract An oxidative catalytic vanadium(V) system was developed to access the naturally nonabundant diastereomers of carpanone from the corresponding alkenyl phenol monomer in one pot by tandem oxidation, oxidative coupling, and 4+2 cyclization. This system was applied to the synthesis of two other analogues of carpanone. Mild oxidizing silver salts were used as the terminal oxidant to minimize background oxidation which produces the natural diastereomer of carpanone. Further, the first examples of enantioselective oxidative benzoxanthenone formation are reported. Solvent polarity has a strong effect on enantioselectivity, consistent with a mechanism involving binding of vanadium Schiff base catalysts to the alcoholic moiety of the alkenyl phenols during the cyclization step. 

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2. Flow Chemistry‐Enabled Divergent and Enantioselective Total Syntheses of Massarinolin A, Purpurolides B, D, E, 2,3‐Deoxypurpurolide C, and Structural Revision of Massarinolin A

   https://doi.org/10.1002/anie.202109625  

   Wang, Ye‐Cheng; Cui, Chengsen; Dai, Mingji (September 2021, Angewandte Chemie International Edition)

   Abstract Massarinolin A and purpurolides are bioactive bergamotane sesquiterpenes condensed with a variety of synthetically challenging ring systems: a bicyclo[3.1.1]heptane, an oxaspiro[3.4]octane, and a dioxaspiro[4.4]nonane (oxaspirolactone). Herein, we report the first enantioselective total syntheses of massarinolin A, purpurolides B, D, E, and 2,3‐deoxypurpurolide C. Our synthesis and computational analysis also led to a structural revision of massarinolin A. The divergent approach features an enantioselective organocatalyzed Diels–Alder reaction to install the first stereogenic center in highee, a scalable flow photochemical Wolff rearrangement to build the key bicyclo[3.1.1]heptane, a furan oxidative cyclization to form the oxaspirolactone, a late‐stage allylic C−H oxidation, and a Myers’ NBSH‐promoted sigmatropic elimination to install theexomethylene group of massarinolin A. 

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3. Cobalt catalyzed multicomponent cyclizations of enynes and alkenes

   Herbort, James; RajanBabu, T. V. (April 2020, Book of Abstracts, 259th ACS National Meeting & Exposition, Philadelphia, PA)

   null (Ed.)

   Synthesis of complex organic molecules has relied heavily on the use of stoichiometric organometallic reagents. Strategies such as metal-catalyzed cycloisomerization bypass the need for these oftentimes harsh reagents and are valuable for constructing cyclic frameworks from simple unsaturated carbon sources. An important extension of this cyclization methodology is the incorporation of additional components accompanying the initial annulation. Through our studies we learned that cationic cobalt complexes can catalyze an intramolecular enyne cyclization, and subsequently form carbon-carbon bonds through intermolecular incorporation of feedstock alkenes into a presumed metallacycle intermediate. This strategy allows access to complex alicyclic and heterocyclic compounds from an earth abundant metal catalyst and readily available materials. Of note, is the complimentary reactivity and selectivity in this newly discovered cationic cobalt reaction manifold as compared to analogous rhodium and ruthenium catalysis. We discovered that product selectivity is dependent upon alkene identity, with activated alkenes and unactivated alkenes inserting into opposite sides of the cobaltacyclopentene intermediate. This remarkable selectivity provides access to two different motifs accompanying the cycle formed, either a linear diene or a styrene with a pendant functionalized acrylate. Over 25 different medicinally relevant pyrrolidines were accessed in this fashion and further elaborated on by post-synthetic modifications. In addition, the enantioselective variant of this reaction is also explored with selectivities up to 77% ee. 

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4. Enantioselective Fluorescent Recognition of β‐Amino Alcohols by Stereoselective Cyclization

   https://doi.org/10.1002/ejoc.202200283  

   Tian, Jun; Yu, Shanshan; Guo, Hongyu; Zhu, Maoshuai; Lu, Kai; Jiang, Yixuan; Yang, Jiaqiao; Yu, Xiaoqi; Pu, Lin (May 2022, European Journal of Organic Chemistry)

   Abstract 2,2’‐Diformyl‐1,1’‐binaphthyl is found to exhibit highly enantioselective fluorescence enhancement in the presence of various β‐amino alcohols and base. It provides a new method to determine the enantiomeric composition of those substrates and has potential for high throughput analysis. Based on detailed spectroscopic analyses, it is proposed that a stereoselective cyclization of a β‐amino alcohol with the probe should occur to form a rigid macrocyclic intermediate, contributing to the greatly enhanced fluorescence. 

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5. Enantioselective total synthesis of (+)-cylindricine B

   https://doi.org/10.1039/D4SC04910A  

   Dukes, Dallas M; Atanassov, Victor K; Smith, Joel M (October 2024, Chemical Science)

   This article describes the first enantioselective synthesis of the Tasmanian marine alkaloid (+)-cylindricine B. The concise construction of the compound hinged on dearomative retrosynthetic logic combined with a tactical advance in the generation of congested, cyclic, alpha-tertiary amine centers. The scope of this key coupling reaction was explored in addition to providing a synthetic application for Cu-catalyzed enantioselective dearomatization of N-acyl-pyridiniums. The synthesis proceeds in five or six steps from commercially available starting materials. 

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