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
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
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DOI：
10.1021/ja037637d
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发表时间：
2003-11-19
影响因子：
15
通讯作者：
Popik, VV
中科院分区：
文献类型：
--
作者：
Bogdanova, A;Popik, VV
重氮Meldrum酸（1）在甲醇溶液中的光化学或热分解产生酮酯3a，这是Wolff重排的产物，而未检测到由单线态卡宾产生的产物。结合对1热分解活化参数的分析，以及DFT B3 PW 91/6-311+G（3df，2 p）和MP2/aug-cc-pVTZ//B3 PW 91/6-311+G（3df，2 p）的计算结果，我们认为1的Wolff重排是一个协同反应过程.重氮米氏酸的光解结果取决于照射的波长。用254 nm光照射导致有效的（Phi（254）= 0.34）光-Wolff反应，而在355 nm下，形成二氮杂环丙烷2成为主要过程（Phi（350）= 0.024）。这种不寻常的波长选择性表明，沃尔夫重排和异构化起源于不同的电子激发态的1。二氮杂环丙烯2的UV照射导致氮的损失和Wolff重排，显然是通过卡宾中间体。该过程伴随着重氮Meldrum酸的逆异构化。这两种异构体的三重态敏化光解导致形成Meldrum酸，其为1和2的形式还原的产物。温和加热二氮丙啶2产生定量产率的重氮Meldrum酸。测定了重氮1和重氮杂环2异构体在水溶液和二氧六环溶液中热反应的活化参数。
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.