The Photo-Favorskii Reaction of p-Hydroxyphenacyl Compounds Is Initiated by Water-Assisted, Adiabatic Extrusion of a Triplet Biradical
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- 作者：Richard S. Givens ; Dominik Heger ; Bruno Hellrung ; Yavor Kamdzhilov ; Marek Mac ; Peter G. Conrad II ; Elizabeth Cope ; Jong I. Lee ; Julio F. Mata-Segreda ; Richard L. Schowen ; Jakob Wirz
- 刊名：Journal of the American Chemical Society
- 出版年：2008
- 出版时间：March 19, 2008
- 年：2008
- 卷：130
- 期：11
- 页码：3307 - 3309
- 全文大小：175K
- 年卷期：v.130,no.11(March 19, 2008)
- ISSN：1520-5126
文摘
The p-hydroxyphenacyl group 1 is an effective photoremovable protecting group, because it undergoes an unusual photo-Favorskii rearrangement concomitant with the fast release (<1 ns) of its substrates in aqueous solution. The reaction mechanism of the diethyl phosphate derivative 1a was studied by picosecond pump-probe spectroscopy, nanosecond laser flash photolysis, and step-scan FTIR techniques. The primary photoproduct is a triplet biradical, 33, with a lifetime of about 0.6 ns. The release of diethyl phosphate determines the lifetime of the triplet state T1(1a), 
fchars/tau.gif" BORDER=0 >(T1) = 60 ps in wholly aqueous solution. Formation of a new photoproduct, p-hydroxybenzyl alcohol (6), was observed at moderate water concentrations in acetonitrile. It is formed by CO elimination from the elusive spirodione intermediate (4), followed by hydration of the resulting p-quinone methide (5). Computational studies show that CO elimination from the spirodione is a very facile process.
fchars/tau.gif" BORDER=0 >(T1) = 60 ps in wholly aqueous solution. Formation of a new photoproduct, p-hydroxybenzyl alcohol (6), was observed at moderate water concentrations in acetonitrile. It is formed by CO elimination from the elusive spirodione intermediate (4), followed by hydration of the resulting p-quinone methide (5). Computational studies show that CO elimination from the spirodione is a very facile process.