D. Schwebel, P. Margaretha
Jun 7, 2000
Citations
0
Influential Citations
6
Citations
Journal
Helvetica Chimica Acta
Abstract
Both (intermolecular) photocycloadditions of 2H-1-benzopyran- and 2H-1-benzothiopyran-3-carbonitriles to 2,3-dimethylbut-2-ene and 2-methylbut-1-en-3-yne, and (intramolecular) photoisomerization of 4-(alkenyl)benzopyran-3-carbonitriles were investigated. In contrast to 2H-1-benzopyran-3-carbonitrile (1), its thia analog 4 reacts with 2,3-dimethylbut-2-ene selectively, to afford only cyclobuta derivative 7. In the presence of 2-methylbut-1-en-3-yne, both 1 and 4 behave alike to afford the all-cis-cyclobuta diastereoisomers, 15 and 8, respectively, as main products, as well as minor amounts of cyclobutenes 17 and 10, respectively, which result from the addition of the terminal C-atom of the acetylenic bond to C(3) of the heterocycle. 4-Methyl-2H-1-benzopyran-3-carbonitrile (5) does not undergo photoaddition to the alkene or the alkenyne mentioned above, whereas the corresponding intramolecular [2+2] photocycloaddition of 4-(pent-4-enyl)benzopyran-3-carbonitrile (6b) to tetracycle 20 proceeds quantitatively.