62609-78-3Relevant articles and documents
Chemistry of diazocarbonyl compounds: XXV. Comparative photochemistry of diazo compounds and sulfur ylides of the 1,3-dioxane-4,6-dione series
Nikolaev,Shevchenko,Platz,Khimich
, p. 815 - 827 (2007/10/03)
Photochemical decomposition of 2,2-dialkyl-5-diazo-1,3-dioxane-4,6-diones in the presence of pyridine, methanol, or dimethyl sulfide as carbene traps involves mainly the Wolff rearrangement which is likely to follow a concerted pattern, while the yield of the "carbene" products does not exceed 27-28%. No carbene intermediates are formed in the photolysis of the corresponding dioxo sulfonium ylides under analogous conditions, and the main photochemical process is 1,2-methyl shift (Stevens rearrangement), followed by photochemical transformations of the primary products according to the Norrish type II pattern. Pleiades Publishing, Inc., 2006.
Experimental and Theoretical Investigation of Reversible Interconversion, Thermal Reactions, and Wavelength-Dependent Photochemistry of Diazo Meldrum's Acid and Its Diazirine Isomer, 6,6-Dimethyl-5,7-dioxa-1,2-diaza-spiro[2,5]oct-1-ene-4,8-dione
Bogdanova, Aneta,Popik, Vladimir V.
, p. 14153 - 14162 (2007/10/03)
The photochemical or thermal decomposition of diazo Meldrum's acid (1) in methanolic solutions yields ketoester 3a, the product of the Wolff rearrangement, while products produced from the singlet carbene were not detected. This observation, combined with the analysis of activation parameters for the thermal decomposition of 1, as well as with the results of DFT B3PW91/6-311+G(3df,2p) and MP2/aug-cc-pVTZ//B3PW91/6-311+G(3df,2p) calculations, allows us to conclude that the Wolff rearrangement of 1 is a concerted process. The outcome of the photolysis of diazo Meldrum's acid depends on the wavelength of irradiation. Irradiation with 254 nm light results in an efficient (Φ254 = 0.34) photo-Wolff reaction, while at 355 nm, the formation of diazirine 2 becomes the predominant process (Φ 350 = 0.024). This unusual wavelength selectivity indicates that Wolff rearrangement and isomerization originate from different electronically excited states of 1. The UV irradiation of diazirine 2 leads to the loss of nitrogen and the Wolff rearrangement, apparently via a carbene intermediate. This process is accompanied by a reverse isomerization to diazo Meldrum's acid. Triplet-sensitized photolysis of both isomers results in the formation of Meldrum's acid, the product of a formal reduction of 1 and 2. Mild heating of diazirine 2 produces quantitative yields of diazo Meldrum's acid. The activation parameters for thermal reactions of diazo 1 and diazirino 2 isomers were determined in aqueous and dioxane solutions.
DYnamics of the Wolf Rearrangement of Six-Membered Ring o-Diazo Ketones by Laser Flash Photolysis
Tanigaki, Katsumi,Ebbesen, Thomas W.
, p. 4531 - 4536 (2007/10/02)
The Wolff rearrangement of six-membered ring o-diazo ketones, 1-oxo-2-diazo-1,2-dihydronaphthalene (DNQ) and its four 4- and 5-sulfonate analogues, 1-ox-2-diazo-1,2-dihydrobenzene (DBQ), and diazoMeldrum (DM), are studied in solution at room temperature by laser flash photolysis.A precursor to a ketene is observed in most cases.It is assigned to be an oxirene on the basis of reactivity, kinetic results and thermodynamic results.The Wolff rearrangement does not involve a concerted mechanism but a stepwise reaction for these types of diazo ketones.Thermodynamic analyses indicate that the activation barriers for the transformation of the oxiranes into ketenes are very low, typically 10-20 Kj/mol, in godd agreement with theoretical predictions in the literature.The observation of oxirene in solution in nanosecond time scales, and longer, is attributed to the low preexponential factors due to the negative entropy of solvatation.The important role of the solvent is further confirmed in the kinetic analysis of ketene formation in various water-methanol mixtures.
