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Keywords:

  • Naphthacenes;
  • Heptacenes;
  • Benzo[c]furans;
  • Cycloadditions;
  • re/si Selectivity

Abstract

Cycloaddition reactions of 1,4-dihydro-1,4-epoxynaphthalenes (2) and benzo[c]furans (4), generated in situ from the tetracyclone adducts of 2, yield the diepoxynaphthacenes 5 (Schemes 1, 2). Out of 4 possible stereoisomers an exo-exo and an exo-endo geometry (A and C in Scheme 3) can be realized. The ratio A:C varies from pure A to pure C depending on the substituents of 2 and 4. Stereoisomeric heptacenes 7 can be obtained by a twofold cycloaddition of the same type (Scheme 4). Only one π bond of reactive alkynes such as cyclooctyne or acetylenedicarboxylate is capable of an addition to 4 (Schemes 5, 6).