Synthesis and Chiroptical Properties of Dimethyl 8,12‐Diphenylbenzo[<i>d</i>]heptalene‐6,7‐dicarboxylate

Abstract

Abstract 6,10‐Diphenylbenz[ a ]azulene ( 3 ) was reacted with dimethyl acetylenedicarboxylate (ADM) in the presence of 2 mol‐% of [RuH 2 (PPh 3 ) 4 ] in MeCN at 100° 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° 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° 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° 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.