Highly efficient trapping of short-lived 1,4-diradicals, the order of first bond formation in the intramolecular photocycloaddition of 3-(4′-pentenyl)-cyclohex-2-enones

✍ Scribed by Dan Becker; Nitsa Galili; Nizar Haddad

• Publisher: Elsevier Science
• Year: 1996
• Tongue: French
• Weight: 264 KB
• Volume: 37
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(96)02053-9

✦ Synopsis

Complete trapping of 1.4~diradical intermediates, formed in the intramolecular [2+2] photocycloaddition of 13. provide direct evidence for the exclusive formation of the first bond at the C(8) of the cyclic enone. This result is found in full agreement with the previously studied compounds 1.

Copyright 8 1996 Elsevier Science Ltd 'lhe intramolecular photocycloaddition of alkenes to cyclic enones of type 1 has been extensively investigated by

Becker and co-workers*. Systematic investigation revealed that similar ratio of the endo (3):exo (4) isomers was obtained in all cases, a 1: 1 ratio was obtained upon irradiation at 250C. In all cases, minor geometrical isomerization of the alkene in the starting material 1 was detected during the irradiation (ca. 10%). Based on these results, they concluded that first-bond formation in these compounds follow the "role of five"2 and takes place exclusively via R+'-Me.