Diethyl ketene acetal, cycloadditions

The first example of a bimolecular 1,3-dipolar cycloaddition between an isomtinchnone and an electron-rich dipolarophile was reported by our group several years ago [27]. The reaction of diethyl ketene acetal and isomtinchnone 9 gave cycloadduct 29 in high yield. Again, only one regioisomer was obtained and the regiochemistry encountered is consistent with cycloaddition involving the HOMO of diethyl ketene acetal and the LUMO of isomunchnone 12 (n = 1). 

Table I records the results obtained in the preparation of 30 cycloaddition products from the acridizinium cation. As was demonstrated by Fields, Regan, and Dignan, even preparative experiments done at different temperatures and in different solvents are adequate to prove the inverse electron demand character of the reaction. Nucleophilic alkenes, like ketene diethyl acetal, reacted in minutes at room temperature while the strongly electrophilic alkene, tetracyanoethylene, failed to react under any conditions.

Truce and Norrell noticed in 1963 that sulfenes readily undergo 2 - - 2 cycloaddition to ketene diethyl acetal with the formation of 3,3-diethoxythie-tane 1,1-dioxides. The same reaction was carried out by Paquette, using 1,1-dioxide ketals with cyclic a-halo sulfones in which the corresponding chloroketal derivatives 47 were formed. This approach may be illustrated by the addition of ketene diethyl acetal to halogenated sulfenes and to... 

The cycloaddition of ketene diethyl acetal to benzo[6]quinolizinium salt 247, followed by hydrolysis and thermolysis, gave over-crowded 1-pyridyl-8-rerf-butylnaphthalene 248. The naphthalene 248 was oxidized electro-chemically or with anhydrous CuCl2 to afford azoniafluoranthene salt 249,... 

CYCLOADDITION Alumina chloride. l,2-Bis(trimethylsilyloxy)cyclo-butene. 2,2-Dimethyl-3(2/T)-furanone. Ethylaluminum dichloride. Ketene diethyl acetaL Methyl cyclobutene-carboxylate. Trimethyl-1,3-diox olen-one. Zinc chloride. 

Coumarin has been studied extensively in this context in the absence of a sensitiser, it gives a syn head-to-head dimer in the presence of benzophenone as sensitiser, the anti isomer is formed the syn head-to-tail dimer is obtained by irradiation in acetic acid. Cyclobutane-containing products are obtained in modest yields by sensitiser-promoted cycloadditions of coumarins or 3-acyl-oxycoumarins, with alkenes, ketene diethyl acetal or cyclopentene. ... 

Benzoylketene diethyl acetal207 has been found to undergo [4 + 2] cycloaddition with phenylsulfene to give a (5-sultone (116) (equation 101), whereas acetyl ketene diethyl acetal gave 118, perhaps via 117 (equation 102)207. 

Recently, Avenoza and Peregrina reported MABR-mediated [2 + 2 + 2]cycload-dition of ketene diethyl acetal with a-amioacrylate (113) and [2 + 2]cycloaddition of... 

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