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1. Mechanochemical Reactivity of a 1,2,4‐Triazoline‐3,5‐dione‐Anthracene Diels‐Alder Adduct

   https://doi.org/10.1002/asia.202300850  

   Chang, Hao‐Chun; Liang, Min‐Chieh; Luc, Van‐Sieu; Davis, Chelsea; Chang, Chia‐Chih (November 2023, Chemistry – An Asian Journal)

   Abstract Force‐responsive molecules that produce fluorescent moieties under stress provide a means for stress‐sensing and material damage assessment. In this work, we report a mechanophore based on Diels‐Alder adductTAD‐Anof 4,4′‐(4,4′‐diphenylmethylene)‐bis‐(1,2,4‐triazoline‐3,5‐dione) and initiator‐substituted anthracene that can undergo retro‐Diels‐Alder (rDA) reaction by pulsed ultrasonication and compressive activation in bulk materials. The influence of having C−N versus C−C bonds at the sites of bond scission is elucidated by comparing the relative mechanical strength ofTAD‐Anto another Diels‐Alder adductMAL‐Anobtained from maleimide and anthracene. The susceptibility to undergo rDa reaction correlates well with bond energy, such that C−N bond containingTAD‐Andegrades faster C−C bond containingMAL‐Anbecause C−N bond is weaker than C−C bond. Specifically, the results from polymer degradation kinetics under pulsed ultrasonication shows that polymer containingTAD‐Anhas a rate constant of 1.59×10⁻⁵ min⁻¹, whileMAL‐An(C−C bond) has a rate constant of 1.40×10⁻⁵ min⁻¹. Incorporation ofTAD‐Anin a crosslinked polymer network demonstrates the feasibility to utilizeTAD‐Anas an alternative force‐responsive probe to visualize mechanical damage where fluorescence can be “turned‐on” due to force‐accelerated retro‐Diels‐Alder reaction. 

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2. Ring Opening Metathesis Polymerization of a New Monomer Derived from a Nitroso Diels–Alder Reaction

   https://doi.org/10.1002/macp.202100098  

   Subnaik, Selesha; Sheridan, Katya; Hobbs, Christopher E. (May 2021, Macromolecular Chemistry and Physics)

   Abstract A nitroso Diels–Alder (NDA) reaction between cyclopentadiene and an in situ generated nitroso compound leads to a new heterocyclic monomer for ring opening metathesis polymerization (ROMP) reactions. This monomer could be polymerized in the presence of Grubbs‐third generation initiator with good control overM_nand decentÐvalues. The resulting isoxazolidine‐containing material could undergo further hydrogenation, deprotection, and modification with Dansyl chloride as well as ring opening to provide an amino‐and hydroxyl‐decorated “polyolefin.” 

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3. Synthesis and structure of 1′,4′-diphenyl-1a,1′,4′,4′′,5′′,9b-hexahydro-2′′ H -dispiro[cyclopropa[ l ]phenanthrene-1,2′-[1,4]epoxynaphthalene-3′,3′′-thiophene]

   https://doi.org/10.1107/S2056989025004104  

   Wen, Yuewei; Thamattoor, Dasan M (June 2025, Acta Crystallographica Section E Crystallographic Communications)

   The title compound, C₃₉H₃₀OS, was inadvertently prepared as a Diels–Alder adduct between 1,3-diphenylisobenzofuran and 3-(1a,9b-dihydro-1H-cyclopropa[l]phenanthren-1-ylidene)tetrahydrothiophene. A combination of fused, bridged, and spirocyclic ring systems are all featured within a single molecular structure of this highly crowded polycyclic compound. 

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4. Diels−Alder Reactions of 1‐Alkoxy-1-amino-1,3-butadienes: Direct Synthesis of 6‐Substituted and 6,6-Disubstituted 2‐Cyclohexenones and 6‐Substituted 5,6-Dihydropyran-2-ones

   https://doi.org/10.1021/acs.orglett.1c01031  

   Elkin, P. K.; Durfee, N. D. (June 2021, Organic letters)

   Gaich, T. (Ed.)

   We report the cycloaddition reactions of 1-alkoxy-1- amino-1,3-butadienes. These doubly activated dienes are prepared on a multigram scale from crotonic acid chloride and its derivatives. The dienes undergo Diels−Alder (DA) and hetero-Diels−Alder (HDA) reactions under mild reaction conditions with a variety of electron- deficient dienophiles to afford cycloadducts in good yields with excellent regioselectivities. The hydrolysis of the DA cycloadducts provides 6-substituted and 6,6-disubstituted 2-cylohexenones, which are versatile building blocks for complex molecule synthesis. The corresponding HDA cycloadducts afford 6-substituted 5,6-dihydropyr- an-2-ones. 

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5. Charge‐activated TADDOLs: Recyclable organocatalysts for asymmetric (hetero‐)Diels–Alder reactions

   https://doi.org/10.1002/poc.4355  

   Riegel, George F.; Takashige, Keiji; Lovstedt, Alex; Kass, Steven R. (May 2022, Journal of Physical Organic Chemistry)

   Abstract Several charge‐containing TADDOL salts were synthesized and used as organocatalysts in asymmetric Diels–Alder and hetero‐Diels–Alder reactions. Their catalytic activity was found to exceed that of a noncharged analog while maintaining or improving upon the enantioselectivity. The enhanced activities of the TADDOL salts enabled them to act as presumed hydrogen bond donor catalysts in the Diels–Alder and hetero‐Diels–Alder reactions of 1,3‐cyclohexadiene with methyl vinyl ketone at 40°C and 2‐phenoxy‐1,3‐butadiene with ethyl glyoxylate at room temperature, respectively. Given the ionic nature of these charge‐activated catalysts, it also proved possible to recycle and reuse the TADDOL without chromatography or the need for a recrystallization. 

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