Photodimerization of dibenz[b,f] azepine derivatives and their reaction intermediates

Substituent‐Dependent Reactivity in the Photodimerization of N‐Substituted Dibenz[b,f]azepines

“…This study clearly establishes the formation of dimers from several dibenzazepines upon direct irradiation, provided the concentration is high or the solid is irradiated (Tables 5, 6). A non-sensitized photodimerization was denied in a previous publication, [11] while another study [1] favors less efficient dimerization without a sensitizer; one paper on carbamazepine 21 is equivocal in this respect: [7] the authors might have irradiated a suspension. Since the brominated compound 11 does not yield photodimers under all conditions, and since the dimeric products are again exclusively anti-dimers, we have to regard them as triplet products, in spite of the low intersystem crossing rates upon direct excitation (according to the flash experiments in dilute solutions).…”

“…[11] Phosphorescence is concluded i) from the long-wavelength onset of the spectrum for 4±7, and ii) from a first-order decay component with a lifetime of 3±5 ms for 4 and 7. From the phosphorescence onset and maxima at l = 500 and 538 nm for 4, a triplet energy of E T = 254 kJ mol À1 was estimated.…”

“…[5] For the non-substituted dibenzazepine (1) and its N-acetyl (10) and N-valeroyl (15) derivatives, low quantum yields of intersystem crossing (F ISC ) were reported. [11] For benzophenone-sensitized excitation of 15, an anti-cyclobutane dimer is formed with a quantum yield of photodimerization of up to F d = 0.15. [11] Non-sensitized photodimerization were reported to be less efficient, [1] a result which was questioned later on by other authors [11] who claimed that direct excitation did not yield dimers at all.…”

“…[11] The selfquenching reaction in Equation (2) is difficult to measure with nanosecond flash photolysis and l exc = 354 nm since low signals are necessary to reduce T±T annihilation of 3 DBA*, the required concentration of DBA is rather high and direct excitation cannot be ignored for 1±7. Several attempts gave only a lower limit, typically k 2 < 3 î 10 7 dm 3 mol À1 s À1 , for example, for 4 or 7.…”

Bioactive cyclobutane-containing alkaloids

“…Under the sensitized conditions, the quantum yield for the photodimerization was established as 0.15 at 25°( DBA = 2.0 · 10 -3 mol/l). The triplet intermediate of this reaction was detected by nanosecond laser photolysis, and the kinetic parameters of the triplet species were detected [180,181]. Gilvocarcin V (also known as antibiotic 1072B, NSC 338943, and NSC 348115), an antitumor agent produced by Streptomyces griseoflavus Goe 3592 and various other streptomycetes, is the most important representative of the distinct family of benzo[d]naphtha [1,2-b] pyran-6-one aryl C-glycoside antibiotics, which show excellent antitumor activity and a remarkably low toxicity [182].…”