SYNTHESIS AND CHIROPTICAL PROPERTIES OF DIMETHYL 8,12-DIPHENYLBENZO[D]HEPTALENE-6,7-DICARBOXYLATE

6, 10-Diphenylbenz[a]azulene (3) was reacted with dimethyl acetylenedicarboxylate (ADM) in the presence of 2 mol- % of [RuH2(PPh3)4] in MeCN at 100-degrees to yield a 7:1 mixture of dimethyl 2,6-diphenyl-9,10-benzotricyclo-[6.2.2.0(1,7)]dodeca-2,4,6,9,11-pentaene-11,12-dicarboxylate (4) and dimethyl 8,12-diphenylbenzo[d]heptalene-6,7-dicarboxylate (5; Scheme 2). The tricycle 4, when heated in DMF at 150-degrees for 1 h led to the formation of 81.5 % of the heptalene-6,7-dicarboxylate 5 and 15 % of the starting azulene 3. No rearrangement of tricycle 4 was observed, when it was heated at temperatures up to 180-degrees in pseudocumene. The heptalene-6,7-dicarboxylate 5 was easily separated into its antipodes (PM)- and (MP)-5 on a Chiracel column (cf. Fig. 2). On heating at 150-degrees for 1 h, (MP)-5 showed no racemization at all. The Ru-catalyzed reaction of benz[a]azulene (6) with ADM led to the formation of dimethyl 9,10-benzotricyclo[6.2.2.0(1,7)]dodeca-2,4,6,9,11-pentaene-11,12-dicarboxylate (7; Scheme 3). However, the formation of the corresponding heptalene-6,7-dicarboxylate could not be observed.