From 3,4-dinitrothiophene to 1,2-diaryl-4-nitrobenzenes through (E,E,E)-1,6-diaryl-3-nitro-1,3,5-hexatrienes

The reactions between 1,2-bis(diethylamino)-2,3-dinitro-1,3-butadiene, easi ly obtainable by ring-opening of 3,4-dinitrothiophene with diethylamine, an d arylmethylmagnesium chlorides in THF at 0 degreesC furnished good yields of (E,E,E)-1,6-diaryl-3-nitro-1,3,5-hexatrienes. To explain the formation o f the hexatrienes, a mechanism is advanced which involves, in particular, t automerisation of the intermediate 1,6-diaryl-3,4-dinitro-2,4-hexadienes fo llowed by base-induced elimination of nitrous acid. The electrocyclic disro tatory conversion of the hexatrienes into the corresponding 5,6-diaryl-2-ni tro-1,3-cyclohexadienes was analysed by H-1 NMR spectroscopy and exploited for the high-yielding synthesis of 1,2-diaryl-4-nitrobenzenes employing, as oxidants, either DDQ or iodine in the presence of cyclohexene oxide as HI scavenger. (C) 2001 Elsevier Science Ltd. All rights reserved.