1- Indenone 2-phenyl-3-

Thermal reactions of N-aryl cyclopropenone imines 268 are differentiated by the nature of the N-aryl substituent. Imines 268 (Ar = phenyl, p-nitro-phenyl) undergo isomerization to N-aryl-2-phenyl-indenone imines 271 when heated in aprotic solvents202. Since in protic solvents, e.g. ethanol, only the iminoester 272 is isolated, evidence seems to be given for the intermediacy of 269 implying carbene and ketene imine functionality, which may either cause electrophilic ring closure with a phenyl group to form 271 or may add to the hydroxylic solvent (272). 

Whilst Lewis acids like SbCls or A1C13 form stable adducts with diphenyl cyclopropenone, from which the ketone can be regenerated unchanged208, trialkyl boranes effect a remarkable ring expansion to 2-phenyl indenone derivatives 309 containing an additional residue in the 3-position215. ... 

This procedure is capable of considerable variation, by which other indenones may be secured. For example, the benzalphthalide may be replaced by other phthalides made from (a) other aldehydes, or (b) other anhydrides the phenyl-magnesium bromide can be replaced by other Grignard reagents. 

Perchloro-l,2,3,-triphenyl-3,4-dihydronaphthalene does not give a qui-none, but indenone [45] instead (27) (Armet, 1978). This result is consistent with the assumption that nucleophilic attack at the initial carbenium centre on the phenylated ring and at C(8) of the nonphenylated ring are sterically hindered. Consequently, the o-quinone [44] is presumably formed, and this undergoes oxidation and degradation, as in the first example. 

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