The Di-Jt-methane Rearrangement and Related Processes

1 The Di-jt-methane Rearrangement and Related Processes. - The crown ether annelated dibenzobarrelene (60) exhibits medium-dependent photochemistry. In solution irradiation affords the COT derivative (61), while in the crystal the di-ji-methane rearrangement occurs to yield the semibullvalene derivative (62). A modification of the normal di-Jt-methane reactivity has been proposed to account for the direct irradiative conversion of deuterium-labelled 7- and 

The tristhienylmethane derivative (63) undergoes photochemical rearrangement. Irradiation in acetonitrile solution through Pyrex at 0°C brings about conversion to the two products (64, 19%) and (65, 46%). The product (64) is formed by a conventional di-Ji-methane rearrangement, which thermally rearranges to afford (65).  

Armesto and his co-workers have demonstrated that electron-transfer induced cyclization of imines (66) follows the di-jr-methane pathway, via the intermediate radical cation (67), to afford the cyclopropane derivatives (68). The outcome of the reaction is to some extent controlled by the electron-transfer sensitizer used, as can be seen in the reported yields. In the biphenyl substituted example, a cyclopropane derivative (69) is formed in competition with an alter- 

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