1,2-Bridged Tricyclic Cyclopropenes: Tricyclo[3.2.1.02,4]octa-2(4),6-diene and Tricyclo[3.2.1.02,4]oct-2(4)-ene

Two 1,2-bridged tricyclic cyclopropenes, tricyclo[3.2.1.0(2,4)]oct-2(4)-ene (6) and tricyclo[3.2.1.0(2,4)]octa-2(4),6-diene (7), have been synthesized by elimination of 2-bromo-4-chlorotricyclo[3.2.1.0(2,4)]octane (17) and 2-bromo-4-chlorotricyclo[3.2.1.0(2,4)]oct-6-ene (8), respectively. Both 6 and 7 were trapped with diphenylisobenzofuran to form two isomers: exo-addition of cyclopropenes and exo-addition of bicyclo[2.2.1]heptenes (exo-exo adducts) and endo-addition of cyclopropenes and exo-addition of bicyclo[2.2.1]heptenes (endo-exo adducts). The stereoselectivity of the Diels-Alder reactions of 6 and 7 with DPIBF is different. The exo-exo/endo-exo ratios of 6 and 7 with DPIBF are 2/1 and 1/2, respectively. Both exo-exo adducts 12 and 18 are stable at refluxing chloroform temperature either with or without DPIBF, but endo-exo adducts 15 and 22 are unstable at room temperature and either isomerize to styrenes 13 and 19 or react with oxygen in the absence of catalyst to generate epoxides 14 and 20. Both styrenes 13 and 19 can be photooxidized by oxygen to give epoxides 14 and 20.