Coumarin (5,6-Benzo-2-pyrone) Trapping of an HDDA-Benzyne

Abstract

Although the parent 2-pyrone is known to react with simple o-benzynes to produce naphthalene derivatives, there appear to be no examples of the successful reaction of coumarin, a benzo-annulated 2-pyrone analogue, with an aryne. We report such a process here using benzynes generated by the hexadehydro-Diels–Alder reaction to produce phenanthrene derivatives (i.e., benzo-annulated naphthalenes). Density functional theory computations were used to help understand the difference in reactivity between 2-pyrone and the slower trapping agent, coumarin. Finally, the reaction of o-benzyne itself [from o-(trimethylsilyl)­phenyl triflate and CsF] with coumarin was shown to be viable, although slow.

Multisubstituted naphthalene synthesis from 4-hydroxy-2-pyrones through [4+2] cycloaddition with o-silylaryl triflates

“…7 a We paid attention to the cyclic ester moiety as a traceless linker that would improve the diene reactivity by fixing the s- cis structure. Although various 2-pyrones served as electron-deficient dienes in the inverse electron-demand Diels–Alder reactions with electron-rich dienophiles such as vinyl ethers 8 and a range of substituted 2-pyrones have served in the reaction with benzyne in recent studies, 7 only limited naphthalenes have been synthesized probably due to the electronic demands as both arynes and 2-pyrones are electron-deficient classes of skeletons, in which substituted arynes were not examined and the effects of substituents on the arynes and pyrones are still unclear. 7 Also, theoretical studies of the aryne reaction with 2-pyrones are sought after.…”

Cycloadditions of Benzynes with the Azoxy [RN═N+(O–)R′] 1,3-Dipole Tautomer of 1-Hydroxybenzotriazole (HOBT)

“…(e) The parent 1,2-dehydrobenzyne produced by the Kobayashi method gives a different regioisomer (see text). [∠s in B from ref , in J from ref , and in K from this work].…”

Divergent Aromatization of α-Halobenzyl γ-Butenolides Initiated by Selective Enol Protonation to Benzo[c]fluorenones and Naphthalenes

“…The high efficiencies of both cascade reactions rely on the de novo formation of an imbedded indenone core. Recently, Hoye and co-workers documented an elegant trapping of indenone-fused benzyne in situ generated by hexadehydro-Diels–Alder reaction with coumarins, which afforded higher π-extended fluorenones upon decarboxylation . In general, rapid and efficient selective synthetic methods for benzo or higher π-extended fluorenones from readily available simple benzenoid substrates are scarce and highly demanding.…”