Wavelength Control in the Photochemical Addition of Tricyclic [g]-Fused 1-Thiocoumarins or Coumarins to Alkenes Yielding Mono- and Bis([2 + 2]-Cycloadducts)
✍ Scribed by Klaus, Christian P. ;Margaretha, Paul
- Book ID
- 102368214
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 417 KB
- Volume
- 1996
- Category
- Article
- ISSN
- 0947-3440
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✦ Synopsis
Abstract
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.