ANNELATED DIMETHYLDIHYDROPYRENES - ELECTROPHILIC SUBSTITUTION AND VALENCE ISOMERIZATION TO METACYCLOPHANEDIENES

The reversible valence isomerization of cyclophanedienes to dihydropyr enes is discussed for a number of [a]- and [e]-annelated examples, 5 - -> 6 and 7 --> 8, and is related to AM1 and MM2+Pi calculations. Only in [e]-fused systems is the isomerization easily seen to be reversible , Electrophilic substitution of dihydropyrenes is discussed. Nitration of the highly annelated 20 gives a mixture of 8- and 7-nitro derivati ves, while NBS/DMF bromination of the benzo[a]dihydropyrene 3 gives mo stly la-bromo derivative.