7-hydroxy-6h-benzo[3,4]cyclobuta[1,2]cyclohepten-6-one. A tropolone condenced with an anti-aromatic four-membered ring

One hundred years of benzotropone chemistry

“…At the same time, Ebine’s group reported the reaction of biphenylene-2,3-quinone ( 560 ) with diazomethane in the presence of boron trifluoride etherate to give another tropolone analogue 561 and its boron difluoride chelate 562 , which was hydrolyzed in acidic aqueous ethanol to 561 quantitatively ( Scheme 101 ) [ 252 – 253 ]. On the other hand, some electrophilic reactions, including nitration, bromination, and azo coupling for 561 yielded only 7-substituted tropolones.…”

“…Although 1,2,5-benzotropoquinone 567 is highly sensitive to moisture, it is stable under anhydrous conditions in the dark and, its hygroscopic form returns to 567 when dried under a vacuum. While the reaction of tropoquinone 567 with o -phenylenediamine gives a quinoxaline derivative 578 , the reduction of 567 to 579 was realized via catalytic hydrogenation with Pd/C ( Scheme 104 ) [ 252 ]. A naphthaldehyde derivative 580 was derived from Thiele acetylation (Ac 2 O, H 2 SO 4 , room temperature) of 567 in 11% yield.…”