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1. 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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2. 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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3. 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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4. Harnessing mechanochemical fluorescence toward autonomous damage-reporting coatings

   https://doi.org/10.1039/d5lp00011d  

   Wang, Zeyu; Zhou, Junfeng; Ling, Zichen; Zhou, Qixin; Wang, Junpeng (May 2025, RSC Applied Polymers)

   A polymer coating autonomously reports damageviafluorescence from a force-induced retro-Diels–Alder reaction. The optical signal correlates with impact energy, enabling real-time, equipment-free damage detection, even in pigmented coatings. 

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5. Total Synthesis of UCS1025A via Tandem Carbonylative Stille Cross Coupling and Diels‐Alder Reaction ^†

   https://doi.org/10.1002/cjoc.202300331  

   Cui, Chengsen; Dai, Mingji (November 2023, Chinese Journal of Chemistry)

   Comprehensive Summary We report an efficient and convergent strategy for the total synthesis of UCS1025A and its diastereomer tetra‐epi‐UCS1025A. UCS1025A is a representative member of the naturally occurring pyrrolizidinone polyketides, from which members with potent antibacterial, antifungal, and anticancer activities have been identified. Our approach features a tandem carbonylative Stille cross coupling and Diels‐Alder reaction to forge a key C—C bond and build thetrans‐decalin system. This tandem process utilizes carbon monoxide as a one‐carbon linchpin to stitch a vinyl triflate and a vinylstannane together and form the desired enone moiety for the subsequent intramolecular Diels‐Alder cyclization. Our synthesis also provides a versatile approach for the synthesis of other related pyrrolizidinone‐containing polyketides. 

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