Document Detail

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.
MedLine Citation:
PMID:  14611254     Owner:  NLM     Status:  MEDLINE    
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 (Phi(254) = 0.34) photo-Wolff reaction, while at 355 nm, the formation of diazirine 2 becomes the predominant process (Phi(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.
Aneta Bogdanova; Vladimir V Popik
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of the American Chemical Society     Volume:  125     ISSN:  0002-7863     ISO Abbreviation:  J. Am. Chem. Soc.     Publication Date:  2003 Nov 
Date Detail:
Created Date:  2003-11-12     Completed Date:  2004-02-13     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  7503056     Medline TA:  J Am Chem Soc     Country:  United States    
Other Details:
Languages:  eng     Pagination:  14153-62     Citation Subset:  IM    
Center for Photochemical Sciences, Bowling Green State University, Bowling Green, OH 43403, USA.
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MeSH Terms
Azo Compounds / chemistry*
Diazomethane / chemistry
Dioxanes / chemistry*
Models, Molecular
Spiro Compounds / chemistry
Grant Support
R15 CA 91856-01A1/CA/NCI NIH HHS
Reg. No./Substance:
0/Azo Compounds; 0/Dioxanes; 0/Spiro Compounds; 2033-24-1/Meldrum's acid; 334-88-3/Diazomethane

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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