Photoreactions of 3-Diazo-3H-benzofuran-2-one; Dimerization and Hydrolysis of Its Primary Photoproduct, A Quinonoid Cumulenone: A Study by Time-Resolved Optical and Infrared Spectroscopy
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- 作者：Yvonne Chiang ; Martin Gaplovsky ; A. Jerry Kresge ; King Hung Leung ; Christian Ley ; Marek Mac ; Gabriele Persy ; David L. Phillips ; Vladimir V. Popik ; Christoph Rö ; dig ; Jakob Wirz ; and Yu Zhu
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：October 22, 2003
- 年：2003
- 卷：125
- 期：42
- 页码：12872 - 12880
- 全文大小：271K
- 年卷期：v.125,no.42(October 22, 2003)
- ISSN：1520-5126
文摘
Light-induced deazotization of 3-diazo-3H-benzofuran-2-one (1) in solution is accompanied byfacile (CO)-O bond cleavage yielding 6-(oxoethenylidene)-2,4-cyclohexadien-1-one (3), which appearswith a rise time of 28 ps. The expected Wolff-rearrangement product, 7-oxabicyclo[4.2.0]octa-1,3,5-trien-8-ylidenemethanone (4), is not formed. The efficient light-induced formation of the quinonoid cumulenone3 opens the way to determine the reactivity of a cumulenone in solution. The reaction kinetics of 3 weremonitored by nanosecond flash photolysis with optical (
max 
460 nm) as well as Raman (1526 cm-1) andIR detection (2050 cm-1). Remarkably, the reactivity of 3 is that expected from its valence isomer, thecyclic carbene 3H-benzofuran-2-one-3-ylidene, 2. In aqueous solution, acid-catalyzed addition of waterforms the lactone 3-hydroxy-3H-benzofuran-2-one (5). The reaction is initiated by protonation of thecumulenone on its 
-carbon atom. In hexane, cumulenone 3 dimerizes to isoxindigo ((E)-[3,3']bibenzofuranylidene-2,2'-dione, 7), coumestan (6H-benzofuro[3,2-c][1]benzopyran-6-one, 8), and a small amountof dibenzonaphthyrone ([1]benzopyrano[4,3-][1]benzopyran-5,11-dione, 9) at a nearly diffusion-controlledrate. Ab initio calculations (G3) are consistent with the observed data. Carbene 2 is predicted to have asinglet ground state, which undergoes very facile, strongly exothermic (irreversible) ring opening to thecumulenone 3. The calculated barrier to formation of 4 (Wolff-rearrangement) is prohibitive. DFT calculationsindicate that protonation of 3 on the -carbon is accompanied by cyclization to the protonated carbene2H+, and that dimerization of 3 to 7 and 9 takes place in a single step with negligible activation energy.
max 460 nm) as well as Raman (1526 cm-1) andIR detection (2050 cm-1). Remarkably, the reactivity of 3 is that expected from its valence isomer, thecyclic carbene 3H-benzofuran-2-one-3-ylidene, 2. In aqueous solution, acid-catalyzed addition of waterforms the lactone 3-hydroxy-3H-benzofuran-2-one (5). The reaction is initiated by protonation of thecumulenone on its -carbon atom. In hexane, cumulenone 3 dimerizes to isoxindigo ((E)-[3,3']bibenzofuranylidene-2,2'-dione, 7), coumestan (6H-benzofuro[3,2-c][1]benzopyran-6-one, 8), and a small amountof dibenzonaphthyrone ([1]benzopyrano[4,3-][1]benzopyran-5,11-dione, 9) at a nearly diffusion-controlledrate. Ab initio calculations (G3) are consistent with the observed data. Carbene 2 is predicted to have asinglet ground state, which undergoes very facile, strongly exothermic (irreversible) ring opening to thecumulenone 3. The calculated barrier to formation of 4 (Wolff-rearrangement) is prohibitive. DFT calculationsindicate that protonation of 3 on the -carbon is accompanied by cyclization to the protonated carbene2H+, and that dimerization of 3 to 7 and 9 takes place in a single step with negligible activation energy.