Electrocyclic reactions of tetraenes

Abstract

Abstract Conjugated tetraenes with both central double bonds of cis configuration undergo a series of thermal reactions, the observable products being markedly dependent on the nature of the terminal substituents. Dimethyl 2E,4Z,6Z,8E-decatetraene-1,10-dioate ( 16 ) was prepared and found to cyclize readily at 50° to trans dimethyl 2,4-bicyclo[4.2.0)octadiene-6,7-dicarboxylate ( 18 ). This reaction proceeds to equilibrium, and the rates and equilibrium constants at the indicated temperatures are: 3.0 × 10 -5 sec -1 −40°; 8.2 × 10 -5 sec -1 , 16.0,50°; −10.0,75°; −7.47,100° with the equilibrium favoring ( 18 ). A sample of 1,8-diphenyl-1E,3Z,5Z;7E-octatetraene ( 1 ) showed no reaction below 120°, and at 175° all trans 1,8-diphenyl-octatetraene, cis and trans stilbenes, trans -5-phenyl-6( cis -styryl)-1,3-cyclohexadiene cis -5-phenyl-6-( trans -styryl)-1,3-cyclohexadiene, and cis and trans 6,8-diphenyl-tricyclo[3.2.1.0 2.7 ]oct-3-enes were formed. At 100° in the presence of excess dimethyl acetylenedicarboxylate 1 gave dimethyl trans -3,4-diphenyltricyclo[4.2.2.0 2.5 ]deca-6,9-dien-6,7-dicarboxylate. Finally 1,4-di(1-cyclohexen-1-yl)-1,3-batadiyne, hydrogenated over a Lindlar catalyst, gave only tricyclo[10.4.0.0 6,11 ]hexadeca-1,3,5-triene.