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Wavelength Control in the Photochemical Addition of Tricyclic [ g ]‐Fused 1‐Thiocoumarins or Coumarins to Alkenes Yielding Mono‐ and Bis([2 + 2]‐Cycloadducts)
Author(s) -
Klaus Christian P.,
Margaretha Paul
Publication year - 1996
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199619960221
Subject(s) - chemistry , irradiation , moiety , alkene , photochemistry , ene reaction , wavelength , molecule , spectroscopy , ring (chemistry) , medicinal chemistry , stereochemistry , organic chemistry , materials science , physics , optoelectronics , quantum mechanics , nuclear physics , catalysis
On long‐wavelength (>395 nm) irradiation in the presence of 2,3‐dimethylbut‐2‐ene the benzobis(thiinones) 6 and 7 afford 4:1 mixtures of cis ‐ and trans ‐fused monocycloadducts. Similarly, irradiation of thiinobenzopyrandione 8 affords 50% of a 4:1 mixture of cis ‐ and trans ‐fused monocycloadducts at the thiinone moiety and in addition further 50% of the cis ‐fused monocycloadduct at the pyranone ring. Irradiation of 6–8 at shorter wavelength (>340 nm) in the presence of the same alkene furnishes mixtures of all bis(photocycloadducts), of which some were isolated by chromatography and analyzed by 1 H‐NMR spectroscopy. – Mixed bis([2 + 2]‐photocycloadducts) of such molecules become easily accessible, as illustrated by the irradiation of benzobispyranone 9 , first (>350 nm) in the presence of 2,3‐dimethylbut‐2‐ene and then (>300 nm) in the presence of isobutene.