Photorearrangements of bridgehead-aryl-substituted dibenzobarrelenes. Steady-state and laser flash photolysis studies

Journal Article · Fri Feb 16 04:00:00 EST 1990 · Journal of Organic Chemistry; (United States)

DOI:https://doi.org/10.1021/jo00291a039· OSTI ID:5974479

Pratapan, S; Ashok, K ^[1]; Gopidas, K R ^[2]; Rath, N P; Das, P K ^[3]; George, M V ^[4]

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1. Indian Inst. of Tech., Kanpur (India)
2. Univ. of Notre Dame, IN (United States) Indian Inst. of Tech., Kanpur (United States)
3. Univ. of Notre Dame, IN (United States)
4. Regional Research Lab., Trivandrum (India) Univ. of Notre Dame, IN (United States) Indian Inst. of Tech., Kanpur (India)

Examples of a novel di-{pi}-methane rearrangement of 9-aryl-substituted dibenzobarrelenes containing 1,2-dibenzoylalkene moieties (1a-f) are presented. Steady-state irradiation of the dibenzobarrelenes 1a-f in benzene gives the regioselectively formed dibenzopentalenofurans, 5a-f, in excellent yields (74-90%). The structure of the bromo derivative 5f was confirmed through X-ray crystallographic analysis. Controlled irradiation of 1b, a representative example, at low temperatures suggests that the dibenzopentalenofurans (5a-f) are formed through the thermal isomerization of the corresponding dibenzosemibullvalenes 6a-f, which, in turn, arise through a di-{pi}-methane type of rearrangement. Laser flash photolysis (337.1 nm) of 1a-f in benzene gives rise to transient phenomena, attributable to dibenzobarrelenes triplets ({phi}{sup T} = 0.2-0.5). These transients are characterized by broad and diffuse absorption spectra and possess short lifetimes (0.13-0.19 {mu}s). They are readily quenched by oxygen, HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy), ferrocene, and {beta}-carotene, with rate constants in the limit of diffusion control (10{sup 8}-10{sup 10} M{sup {minus}1} s{sup {minus}1}).

• OSTI ID: 5974479
• Journal Information: Journal of Organic Chemistry; (United States), Journal Name: Journal of Organic Chemistry; (United States) Vol. 55:4; ISSN JOCEA; ISSN 0022-3263
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400500* -- Photochemistry
ABSORPTION SPECTRA
ALKENES
AROMATICS
BENZENE
CHEMICAL PREPARATION
CHEMICAL REACTIONS
COHERENT SCATTERING
CYCLOALKENES
DECOMPOSITION
DIFFRACTION
ELECTROMAGNETIC RADIATION
ELEMENTS
FURANS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
KETENES
LASER RADIATION
MOLECULAR STRUCTURE
NMR SPECTRA
NONMETALS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OXYGEN
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADIATIONS
REACTION INTERMEDIATES
SCATTERING
SPECTRA
SYNTHESIS
TERPENES
ULTRAVIOLET RADIATION
X-RAY DIFFRACTION