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).
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Meier et al. (1997) studied this question.
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