Benzocyclobutene Derivatives as Intermediates

Several benzannelated compounds have been isolated from natural sources and synthesized. However, only one general method, as described below, has been devised for their preparation. 

IV Ring Expansion from Four-membered Rings 

Compounds of type IV/108 may be opened by reaction with a base in aprotic solvent to give the ring enlarged product in very good yield [56] [59]. This also demonstrates that IV/104 and IV/105 are in equilibrium. Prolongation of the reaction time only leads to higher yields of IV/107 and ring opened IV/110 and with a lower amount of IV/108. 

The reaction can be carried out in two solvents, tetrahydrofuran and 1,2-dime-thoxyethane (DME). DME allows condensations at lower temperatures but also favors the formation of benzocyclobutenoates IV/108. The non-nucleo- 

The arynic condensation, yields of ring enlargement products IY/113. For additional informations see ref. [61] [62]. 

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