Phenyl substituted heterocycles, nitration

This review was originally intended to cover electrophilic substitution in phenyl-substituted heterocycles in general. However, it was decided to concentrate on nitration since this provides the substantial majority of studies in this area. It is the only reaction that seems to have been systematically investigated to any extent and is the only reaction for which there are data for a wide range of phenyl-substituted heterocycles. The literature has been searched to 1991. However, few references have been found in the last 5 years. 

Although nitration has been studied for many years, little systematic work seems to have been carried out in the area of phenyl-substituted heterocycles. There has been a report, Nitration of Phenyl Substituents of Heterocyclic Nuclei (30JCS397) but this only describes afew examples... 

Sec. II.B] NITRATION OF PHENYL-SUBSTITUTED HETEROCYCLES 239 5. Oxazoles and Isoxazoles... 

There are also few reports of the nitration of phenyl derivatives of large ring heterocycles. 7-Chloro-5-phenyl-l//-thieno[2,3- ]-l, 4-diazepin-2(3//)-one (92a) is nitrated to yield the 6-nitro derivative (92b) without phenyl substitution. 5-Phenyl-l-//-thieno[2,3-c]-l, 4-diazepin-2(3 )-one (91c) undergoes both nitration and chlorination to give 7-substituted products also without the formation of nitrophenyl derivatives (73M704, 73M709). 

---