Dimethylaluminum selenide

Selenoaldehydes 104, like thioaldehydes, have also been generated in situ from acetals and then directly trapped with dienes, thus offering a useful one-pot procedure for preparing cyclic seleno-compounds [103,104], The construction of a carbon-selenium double bond was achieved by reacting acetal derivatives with dimethylaluminum selenide (Equation 2.30). Cycloadditions of seleno aldehydes occur even at 0 °C. In these reactions, however, the carbon-selenium bond formed by the nucleophilic attack of the electronegative selenium atom in 105 to the aluminum-coordinated acetal carbon, may require a high reaction temperature [103], The cycloaddition with cyclopentadiene preferentially gave the kinetically favorable endo isomer. 

Cyclic acetals 7 and 9 with one exocyclic oxygen atom react with bis(dimethylaluminum)selenide in the presence of cyclopentadiene at 100 JC giving the cycloadducts 8 and 10, each having a hydroxy group at the terminal position108. Similarly, the reaction of dihydropyranyl methyl acetal 11 affords the Diels-Alder adduct 12 with a side chain having a terminal formyl group108. 

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