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Photocycloaddition of 2 H ‐1‐Benzopyran‐3‐carbonitriles and 2 H ‐1‐Benzothiopyran‐3‐carbonitriles to Alkenes and Alkenynes
Author(s) -
Schwebel Dirk,
Margaretha Paul
Publication year - 2000
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20000607)83:6<1168::aid-hlca1168>3.0.co;2-y
Subject(s) - chemistry , benzopyran , intramolecular force , photoisomerization , alkene , intermolecular force , diastereomer , derivative (finance) , stereochemistry , isomerization , medicinal chemistry , organic chemistry , molecule , catalysis , financial economics , economics
Both (intermolecular) photocycloadditions of 2 H ‐1‐benzopyran‐ and 2 H ‐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 2 H ‐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‐2 H ‐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.