More Like this

1. 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. 

   more » « less
2. Catalytic generation of ortho -quinone dimethides via donor/donor rhodium carbenes

   https://doi.org/10.1039/d3sc00734k  

   Gao, Mingchun; Ruiz, Jose M.; Jimenez, Emily; Lo, Anna; Laconsay, Croix J.; Fettinger, James C.; Tantillo, Dean J.; Shaw, Jared T. (June 2023, Chemical Science)

   Substrates engineered to undergo a 1,4-C–H insertion to yield benzocyclobutenes resulted in a novel elimination reaction to yieldortho-quinone dimethide (o-QDM) products that undergo Diels–Alder or hetero-Diels–Alder cycloadditions. 

   more » « less
3. Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity

   https://doi.org/10.1002/anie.201803872  

   Xiao, Xiao; Woods, Brian P.; Xiu, Wen; Hoye, Thomas R. (July 2018, Angewandte Chemie International Edition)

   Abstract The reaction of an aryne with an alkyne to generate a benzocyclobutadiene (BCB) intermediate is rare. We report here examples of this reaction, revealed by Diels–Alder trapping of the BCB by either pendant or external electron‐deficient alkynes. Mechanistic delineation of the reaction course is supported by DFT calculations. A three‐component process joining the benzyne first with an electron‐rich and then with an electron‐poor alkyne was uncovered. Reactions in which the BCB functions in a rarely observed role as a 4π diene component in Diels–Alder reactions are reported. The results also shed new light on aspects of the hexadehydro‐Diels–Alder reaction used to generate the benzynes. 

   more » « less
4. Evolution of the Diels–Alder Reaction Mechanism since the 1930s: Woodward, Houk with Woodward, and the Influence of Computational Chemistry on Understanding Cycloadditions

   https://doi.org/10.1002/anie.202001654  

   Houk, Kendall N.; Liu, Fang; Yang, Zhongyue; Seeman, Jeffrey I. (January 2021, Angewandte Chemie International Edition)

   Abstract This review article describes the evolution of Woodward's mechanistic thinking, beginning in the late 1930s and early 1940s with his proposal of a charge‐transfer mechanism for the Diels–Alder reaction, eventually leading to the Woodward–Katz two‐stage concerted mechanism in 1959, and then to its mechanistic solution in terms of orbital symmetry control. Houk′s research in the Woodward labs, testing the predictions of this theory, is described. Subsequent modern calculations with quantum mechanics and molecular dynamics simulations have shown that Woodward indeed had perfectly described not only the cyclopentadiene dimerization mechanism, but a new class of transition states now known as ambimodal or bis‐pericyclic transition states. In recent years, the Houk group has found that ambimodal reactions are operative in the [6+4] cycloaddition. Molecular dynamics simulations of many Diels–Alder and ambimodal cycloadditions provide a time‐resolved picture of how these reactions occur. Lastly, Roald Hoffmann provides a Coda in which he describes his joy in “being taken along the journey” of the cycloaddition story from Woodward's youth to today's trajectory simulations. 

   more » « less
5. 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. 

   more » « less