Pyrrole 1-phenyl-, ring synthesis

The synthesis of tripyrazolylmethane and similar reactions of N-magnesium bromide derivatives of pyrazoles (see below) show that the reactive center cannot be transferred from nitrogen to the a-position of the ring as with pyrrole.719-722 Unlike the CH-group of triphenyl-methane, that in tri-l-pyrazolylmethane is not labile.719 The 1-pyrazolyl group is presumably a weaker electron acceptor than a phenyl group because the electron pair of the 1-nitrogen atom is not completely withdrawn into the aromatic system. 

A synthesis of the 2,4-dioxa-10-azatricyclo[6,3,0,0 - ]undecane ring system (17) (Table 2) has been achieved through a photocycloaddition reaction of 4-ethoxycarbonyl-5-phenyl-l//-pyrrole-2,3-dione with a dihydrofuran <87CPB4730>. 

---