Aldehydes diarylmethanes

Benzo[h] thiophene undergoes selective Rieche formylation (65%) in the 3-position with dichloromethyl butyl ether and TiCl4.508 2-Bromo- and 3-methylbenzo[h]thiophene are similarly formylated in the vacant thiophene position.345 508 The diarylmethane compounds 121 (Ar = thiophene, benzo-[h]thiophene, or benzene) undergo Rieche formylation, but the resulting aldehyde cyclizes under the conditions of the reaction, to give the annelated products 122.509... 

Such reactions, which will not be discussed further here, include the formation of diarylmethanes from an aldehyde and two molecules of an aromatic hydrocarbon, of triphenylmethane derivatives from an aldehyde and two molecules of an aromatic amine, and of phthaleins from phthalic anhydride and two molecules of phenol or resorcinol. 

---