AbstractBei der Behandlung mit Dichlorcarben (II) erhält man aus Norbornadien (I) das Addukt (III), das mit Tributylzinnhydrid zu den isomeren Monochloriden (IV) und (V) reduziert wird.

AbstractDifluorcarben (II) reagiert mit Benzobarrelen (I) zu den isomeren Addukten (III) und (IV), wobei beim Erwärmen etwas (IV) aus (III) gebildet wird.

AbstractThe addition of difluorocarbene to bicyclo[2.2.2]octa‐2,5‐diene gave the exo and endo 1:1 cyclopropane adducts. In contrast to norbornadiene, no homo‐1,4 adduct was formed. The adducts were thermally stable under the conditions of their formation and separation (<170°). However, smooth equilibration was achieved on heating at 250° for 36 h. The same mixture resulted from either isomer. At 250° ΔΔG = 1.83 kcal/mol; the endo isomer being the more stable. Heating to higher temperatures caused decomposition, rather than further reaction to the intramolecular [2+2]cyclization products. The kinetic and thermodynamic product compositions were essentially the same on extrapolating to the same temperature, viz. endo/exo = 19–22 at 25°. The mechanisms by which the cyclo‐addition and the stereomutation of the cis‐fused cyclopropane moiety occur are discussed.