Intramolecular SRN1 process

The photostimulated reaction of 1,8-diiodonaphthalene with p-methyl-benzenethio-late ions in DMSO yields the substituted cyclized product 10-methyl-7-thia-benzo[de] anthracene (31) in moderate yield (Scheme 10.58) [54], The mechanism proposed to explain product 31 involves an intramolecular radical cyclization after monosubstitution in the propagation cycle of the SRN1 process. 

The reaction generally proceeds in good yield and could involve an addition-elimination, though the regiochemistry appears to be incorrect for this. An alternative would be an SRN1 process involving (86). The reaction has been applied to the preparation of (87) from the silacyclopropene photolysis then leads to the novel tetracycle (88) through an intramolecular [2+ 2]-cyclo-addition 87>. 

Intramolecular nucleophilic substitution by the anions of o-haloanilides is another viable oxindole synthesis. This is a special example of the category Ic process described in Section 3.06.2.3. The reaction is photo-stimulated and the mechanism is believed to be of the electron-transfer type SRN1 rather than a classical addition-elimination mechanism. The reaction is effective when R = H if 2 equivalents of the base are used to generate the dianion (equation 202) (80JA3646). 

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