Fulvenes and thermochromic ethylenes. Part LXXXIII. ‘Double dibenzotropones’ within C₆-C₇-C₆-C₇-C₆ ring systems. Synthesis of bisbenzo[4,5]cyclohepta[1,2-a:2′,1′-d]benzene-5,7-dione and bisbenzo- [4,5]cyclohepta[1,2-a: 1′,2′d] benzene-5,13-dione

Condensation of pyromellitic anhydride with phenylacetic acid (2 mol. equiv.) gave the two isomeric di-γ-lactones of 4,6-bis-(a-hydroxystyryl)isophthalic acid (IX) and 2,5-bis-(a-hydroxystyryl)terephthalic acid (X) in the ratio of 5:3. 4,6-Bis-(2-phenylethyl)isophthalic acid (XI) and 2,5-bis-(2-phenylethyl)terephthalic acid (XIII), formed by reduction of (IX) and (X), respectively, have been cyclized and dehydrogenated to bisbenzo[4.5]- cyclohepta[1,2-a:2’.1’-d]benzene-5,7-dione (III) and bisbenzo[4.5]cyclohepta[1,2-a:1’.2’-d]benzene-5,1 3- dione (IV).