First measurements of absolute rate constants for oxacarbene intermediates produced in the photochemistry of benzocyclobutenedione

Photochemistry of 1,2,3‐indanetrione*

“…Two separate lines of evidence argue against path a: (i) both thermolysis and photolysis of 11 lead to loss of two molecules of C 0 2 to generate benzyne (Jones and Decamp, 1971) which in turn reacts with electron deficient olefins and dienes to give 2 + 2 and 4 + 2 cycloaddition products, respectively; (ii) photolysis of 1 ,2-benzocyclobutendione (4) under nitrogen leads to products 5 and 6 Ipaktschi, 1966, 1968). In acetonitrile, in either nitrogen degassed or in aerated solutions, photolysis of 4 gives the oxacarbene 13, which may involve the intermediacy of biradical 10 (Boate et al, 1990). Oxacarbene 13 could be formed via path c; however, this carbene is believedto have a singlet ground state and should be rather unreactive towards oxygen (Boate et al, 1990).…”

“…In acetonitrile, in either nitrogen degassed or in aerated solutions, photolysis of 4 gives the oxacarbene 13, which may involve the intermediacy of biradical 10 (Boate et al, 1990). Oxacarbene 13 could be formed via path c; however, this carbene is believedto have a singlet ground state and should be rather unreactive towards oxygen (Boate et al, 1990). However, a note of caution is due here, since other singlet carbenes which are unreactive towards oxygen in the short time scale of laser experiments are known to react with oxygen under different (e.g.…”

5.16 Cyclobutene Ring Opening Reactions

“…The carbene 350 lived for about 20 ms in toluene and could be trapped by typical carbene scavengers such as alcohols. 162 A stereoisomeric mixture of the benzylidenebenzocyclobutenone 351 underwent photoinduced isomerization via the intermediate ketene-allene 352, which had a lifetime of B26 ms (Scheme 136). 163 …”

Adamantanethione

“…42 Similarly, the oxocarbene generated by photo-rearrangement of benzocyclobutenedione is trapped by 1. 43 eq 11Strongly electrophilic dihalocarbenes add easily to 1 leading to the corresponding gem-dihalogenated thiiranes. Dichlorocarbene can be generated conveniently either by thermal decomposition of (trichloromethyl)phenyl mercury (Seyferth reagent) or by elimination of hydrogen chloride from trichloromethane in a two-phase system (Makosza reaction).…”