ISSN:
0009-2940
Keywords:
[2 + 2] Photocycloaddition
;
Selectivity, stereo-, regio-
;
1,4-Biradicals
;
INADEQUATE
;
Calculations, AM1, FINITE
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Stereoselectivity in Photocycloaddition Reactions, 5[1]. - Photoreaction of 2-Cyclopenten-1-one with Enol EthersThe regio- and stereoselectivity of [2 + 2] photocycloaddition reactions between 2-cyclopenten-1-one (1) and the electron-rich alkenes: ethyl, isopropyl, and phenyl vinyl ether (2-4) as well as 2,3-dihydrofuran (10) were examined. In all cases the annulated cyclobutene derivatives 5-7 and 11 were isolated in yields between 70 and 99%. The regioisomeric HT/HH products were formed in a ratio of 3:1 to 4:1. For the determination of the product stereochemistry, INADEQUATE and 1H,1-decoupling experiments were performed. Computer-assisted investigations on the molecular geometry and 1H,1H-coupling constants were performed by using semiempirical methods (AM1, FINITE). The HT regioisomers were formed with moderate endo diastereoselectivity, whereas in the case of the HH regioisomers both diastereomers (exo/endo) were formed in equal amounts. Photoreaction with 2,3-dihydrofuran (10) led to almost exclusive formation of exo-diastereomeric HH and HT regioisomers 11. The observed stereoselectivity is rationalized by the optimal geometry of the intermediate triplet 1,4-biradicals during intersystem crossing.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19921250427
Permalink
