Phototransposition Reactions of Arylboronate Esters in Acetonitrile and 2,2,2-Trifluoroethanol

Autor:	James A. Pincock, Alexandra L. Pincock, K S Cameron, Alison Thompson
Rok vydání:	2004
Předmět:	chemistry.chemical_compound Quenching (fluorescence) Cyclohexane chemistry 2 2 2-Trifluoroethanol Excited state Organic Chemistry Carbon-13 Fluorescence spectrometry Singlet state Acetonitrile Photochemistry Medicinal chemistry
Zdroj:	The Journal of Organic Chemistry. 69:4954-4960
ISSN:	1520-6904 0022-3263
DOI:	10.1021/jo040123s
Popis:	The phototransposition (para, meta, ortho) reactions of the arylboronate esters 4-, 3-, and 2-(4',4',5',5'-tetramethyl-1',3',2'-dioxaborolanyl)toluenes (1, 2, and 3, respectively) in both acetonitrile and 2,2,2-trifluoroethanol (TFE) using 254 nm irradiation have been examined. The irradiations resulted in steady-state compositions of para (5%), meta (19%), and ortho (76%) isomers in acetonitrile starting from the ortho isomer and para (12%), meta (54%), and ortho (35%) isomers in TFE starting from the para isomer. Analysis of the (13)C NMR spectrum of the product mixture obtained from the photochemistry of the para isomer selectively deuterated at C3 and C5 (1d(2)()) revealed that the boron-substituted carbon is the active one in the phototransposition reactions in both acetonitrile and TFE. Similar results were observed for irradiations of 1 in cyclohexane. Fluorescence spectra, singlet-state lifetimes, and Stern-Volmer quenching of fluorescence with 2,3-dimethyl-1,3-butadiene indicated that the excited singlet states of these three isomers were spectroscopic minima and that the excited singlet state was the reactive one for 3 in acetonitrile.
Databáze:	OpenAIRE
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