Trapping Reactions of 1,3-Bridged Cyclopropenes

Article abstract of DOI:10.1021/jo00041a008

The reactive bicycloalk-1(ω)-enes (n = 3-6) 9a-d are formed by dehydrochlorination of 8a-d and trapped by diphenylisobenzofuran as exo Diels-Alder adducts 10a-d.With 8c the major adduct, 18 results not from interception of 9c but from diene 16 that is formed by dehydrochlorination/rearrangement sequences.Attempted interception of cylopropenes 9a-d by furan provides a <4 + 2> product 19 from 9b (n = 4) only.Under the conditions employed, 9a (n = 3) ring expands to carbene prior to furan trapping while homologues 9c and 9d ( n > 4) rearrange and lose HCl too give 17 and 20, respectively, without intervention of furan. 7-Chlorobicyclo<4.1.0>hepta-1(7),3-diene is likewise captured by diphenylisobenzofuran as 13.