Abstract:The Synthesis and the Thermal Decay of 1,2-Diazabenzo(e)semibullvalene and its Relation to the Thermolysis of
BenzobenzvaleneThe [4 + 21-photoadduct of naphthalene and 4-phenyl-4H-l,2,4-triazol-3,5-dione (PTAD) was subjected to a triplet-sensitized di-n-methane rearrangement. Hydrolysis of the resulting urazol15 gave a stable semicarbazide 16 which by nickel-peroxide oxidation gave 1,2-diazabenzo[e]semibullvalene (10). At 40"C, the latter decays in CHCI, solution to produce benzofulvene (2) as the principal pr… Show more
“…Several years ago Sheridan described the photochemical reaction of MeTAD ( 1 ) with a number of aromatic compounds including benzene and naphthalene ( 2 ). , The reactions with benzene and 2 afforded novel Diels−Alder cycloadducts (eq 1) that have served as precursors to several theoretically interesting molecules. − …”
MeTAD thermally reacted with naphthalene (2) and methylated naphthalenes to give equilibrium mixtures of starting materials and [4 + 2] cycloadducts. Methyl substitution on the naphthalene ring generally increased both the amount of cycloadduct formed and the rate of cycloaddition relative to 2. The isolated cycloadducts were all thermally labile and quantitatively reverted to the parent naphthalene in the presence of 2,3-dimethyl-2-butene as a trap for liberated MeTAD. The rates of the cycloreversion reactions were affected by substitution patterns but not appreciably by solvent. A mechanism for the cycloaddition reaction is presented that proposes the involvement of a charge-transfer complex. Photochemically, MeTAD demonstrated lower regioselectivity in its reactions with substituted naphthalenes relative to the corresponding thermal reactions.
“…Several years ago Sheridan described the photochemical reaction of MeTAD ( 1 ) with a number of aromatic compounds including benzene and naphthalene ( 2 ). , The reactions with benzene and 2 afforded novel Diels−Alder cycloadducts (eq 1) that have served as precursors to several theoretically interesting molecules. − …”
MeTAD thermally reacted with naphthalene (2) and methylated naphthalenes to give equilibrium mixtures of starting materials and [4 + 2] cycloadducts. Methyl substitution on the naphthalene ring generally increased both the amount of cycloadduct formed and the rate of cycloaddition relative to 2. The isolated cycloadducts were all thermally labile and quantitatively reverted to the parent naphthalene in the presence of 2,3-dimethyl-2-butene as a trap for liberated MeTAD. The rates of the cycloreversion reactions were affected by substitution patterns but not appreciably by solvent. A mechanism for the cycloaddition reaction is presented that proposes the involvement of a charge-transfer complex. Photochemically, MeTAD demonstrated lower regioselectivity in its reactions with substituted naphthalenes relative to the corresponding thermal reactions.
“…Indeed, a cycloreversion of 1 with intermediate formation of a diazo compound 11 can account perfectly well for the three hydrocarbons 8, 9, and 4 formed by the thermal decay reaction. Although the diazo intermediate 11 was not directly observed in our experiments, its formation has ample precedent [6b] [7] [18] [19]. In particular, we have intercepted (indeny1)diazomethane 13 as adduct 14 to methylacrylate during the thermolysis of 1,2-diazabenzo[e]semibullvalene 15 [20].…”
“…Concentrating on denitrogenation reactions of highly strained systems [7], we were interested in the synthesis of the title diazene 1 and, further, its potential denitrogenation products. In this communication, we wish to report how the target skeleton of 1 can be assembled in a tandem of light-induced reactions; the initial photo-Diels-Alder addition being followed immediately by a di-n -methane rearrangement [S].…”
1 3.1X. 89) ~~ ~ ~~ ~Starting from dibenzo [u,c]cyclooctene (4) and 4-methyl-3H-1,2,4-triazol-3,5(4H)-dione (MTAD), the strained skeleton of the title azo compound 1 is assembled in a tandem photo-Diels-Alder addition/di-n-methane rearrangement sequence. The synthesis is completed by a stepwise hydrolytic oxidation of the ensuing triazolidinedione 2 with nickel peroxide. Thermolysis of 1 in benzene solution is shown to be governed by an initial 1,3-dipolar cycloreversion which leads, via an intermediate diazo compound 11, to cyclobuta[l]phenanthrene 8 and two further carbene-derived C,,H,, products. Photolysis of 1 at 350 nrn leads in modest yield (12%). viu a diazenyl diradical, to an unstable bridged bicyclobutane 10 (dibenzooctavalcne). MNDO calculations suggest the latter to have a rapidly inverting, twisted structure of Cz symmetry.
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