1-(Dialkylamino)isobenzofurans: Generation and Use for Annelation of Aromatic Rings

Article abstract of DOI:10.1021/jo00367a014

Three methods are reported for the generation of the heretofore unreported 1-(dialkylamino)isobenzofurans.These are (1) metal-catalyzed decomposition of an o-(diazomethyl)benzamide (9 to 3), (2) fluoride-induced α elimination of an o-benzamide (48 to 3), and (3) deprotonation of a cyclic imidate salt (51 to 3).The first two reactions are consistent with the intermediacy of a carbene.The precursors for all three approaches can be synthesized from tertiary benzamides by ortho-lithiation strategies.Reaction of the transient 1-(dialkylamino)isobenzofurans with dieneophiles in a ?⁴s + ?²s cycloaddition is the key step in a one-pot sequence that provides annelation of an aromatic ring by a 2,3-substituted 1-(dialkylamino)-4-hydroxycyclohex-1-ene ring.The sequence of formation of the 1-(dialkylamino)isobenzofuran, regio- and stereospecific cycloaddition, ring opening, and proton transfer, is illustrated by the preparations of 15-23, 32, and 33 from N,N-diisopropylbenzamides.The ring annelation is extended to naphthalene and pyridine rings to provide 40, 41, and 44, respectively.Transformations of annelated products to higher and lower oxidation states are reported.