On the mechanism of the photochemical rearrangement of 3-phenyl substituted cyclopropenes to indenes

✍ Scribed by Albert Padwa; Roman Loza; Daniel Getman

• Publisher: Elsevier Science
• Year: 1977
• Tongue: French
• Weight: 201 KB
• Volume: 18
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)83090-2

✦ Synopsis

During the course of our studies dealing with the photochemical transformations of small ring compounds, we uncovered an unusual substituent effect on the mode of ring opening of an unsymmetrically substituted cyclopropene. 192 Thus, the major product obtained from the irradiation of 1 was derived from the preferential cleavage of the cyclopropene single bond which is methyl rather than phenyl substituted. 3,4 Similarly, irradiation of methylphenylcyclopropene Ph R 4 3 afforded a 4:l mixture of indenes 2 and g.5 Two fundamentally different mechanisms were proposed to account for product formation and are outlined in Scheme I. Path A involves cyclopropene ring opening to give a butadienyl carbene followed by electrocyclic closure. The alternate path (B) involves n-s bridging of the excited cyclopropene to give a diradical intermediate which subsequently this communication we wish to is the preferred process.

cleaves to produce the 1,3_cyclopentadiene ring system.