A simple and efficient synthesis of cisoid, transoid, transoid- and all-cisoid-trimers of benzocyclobutene; a novel formation of Z,Z,Z-tribenz[12]annulene from the latter trimer

The cisoid, transoid, transoid- and all cisoid-trimers of benzocyclobutene were synthesised from 1,2-dibromo-1,2-dihydrobenzocyclobutene using nickel-catalysed cyclo-trimerisation; thermal ring-opening of the all-cisoid-trimer gave Z,Z,Z-tribenzo[a,e,i]cyclododedcene (Z,Z,Z-tribenz[12]annulene) which can be converted into its silver and chromium complexes.