18800-15-2Relevant articles and documents
Heterocyclic Aromatic Non-Kekule Molecules. Synthesis and Solution-Phase Chemistry of the Singlet Biradicals 3,4-Dimethylenefuran and 3,4-Dimethylenethiophene
Stone, Keith J.,Greenberg, Marc M.,Blackstock, Silas C.,Berson, Jerome A.
, p. 3659 - 3671 (1989)
The title biradicals 1 and 2 are generated in solution by thermal or photochemical decomposition of the corresponding diazenes, 1,4-dihydrofuranopyridazine (15) and 1,4-dihydrothienopyridazine (16), whose syntheses are described.The biradicals both dimerize, but in the presence of trapping agents, both react with electron-deficient alkenes to form furano(thieno)cyclohexanes (fused adducts).The furan biradical 1, however, gives predominantly a bridged adduct.The cycloadditions are strictly stereospecific and seem to occur by concerted four-centertransition states.Competition studies show that the relative reactivities of alkenes toward the thiophene biradical 2 are quantitatively the same whether the biradical is generated from the diazene precursor 16 or from diallenyl sulfide 6.The latter observation confirms earlier proposals in the literature that biradical 2 could be involved in the chemistry of 6.The reactivity order of the biradicals parallels that of cyclopentadiene toward the test series of alkenes, the selectivities in both series showing a near-unit slope in a bilogarithmic plot, despite the factor of 1E10 by which the biradical absolute rates exceed those of the diene.
Synthesis of the core framework of the cornexistins by intramolecular Nozaki-Hiyama-Kishi coupling
Aimon, Anthony,Farrugia, Louis J.,Stephen Clark
, (2019/08/01)
A new and direct approach to the construction of the core framework of the herbicidal natural products cornexistin and hydroxycornexistin has been developed. Formation of the nine-membered carbocycle found in the natural products has been accomplished by an intramolecular Nozaki-Hiyama-Kishi reaction between a vinylic iodide and an aldehyde. Good yields of carbocyclic products were obtained from the reaction, but diastereomeric mixtures of allylic alcohols were produced. The cyclisation reaction was successful irrespective of the relative configuration of the stereogenic centres in the cyclisation precursor.
Synthetic studies on the cornexistins: Synthesis of (±)-5-epi- hydroxycornexistin
Clark, J. Stephen,Northall, John M.,Marlin, Frederic,Nay, Bastien,Wilson, Claire,Blake, Alexander J.,Waring, Michael J.
supporting information; experimental part, p. 4012 - 4025 (2009/06/27)
The synthesis of 5-epi-hydroxycornexistin (44), a diastereoisomer of the herbicidal natural product hydroxycornexistin (2) has been completed. Palladium mediated sp2-sp3 coupling of the stannane 25 and the chloride 31 and ring-closing metathesis of the resulting diene 32 has been used to construct the tricyclic lactone 34a, which possesses the nine-membered carbocyclic core found in the natural product, in good yield. The synthesis of 5-epi-hydroxycornexistin (44) has established the feasibility of using a furan as precursor for the cyclic anhydride unit present in the natural product and has demonstrated the viability of other late-stage transformations that will be used to prepare hydroxycornexistin (2). The 2008 Royal Society of Chemistry.
