Diels-Alder cycloaddition reactions of 1,1-dichloro-2,3,4,5-tetraethylgermole and 1-chloro-2,3,4,5-tetraethylphosphole with maleic anhydride and maleimide

The Diels-Alder reaction of 1-chloro-2,3,4,5-tetraethylphosphole with maleic anhydride and with maleimide yields 4-chloro-1,7,8,9-tetraethyl-4-oxa-10-phosphatricyclo[5.2.1.0(2),(6)] deca-8-ene-3,5dione ( 1) and 4-chloro- 1,7,8,9-tetraethyl- 4-aza-10-phosphatricyclo[ 5.2.1.02,6] deca-8-ene-3,5dione ( 2). The molecular structure of 1 confirms the formation of the endo-cyclo-adduct with the chlorine atom in an anti-position to the C=C double bond. In contrast to this chlorophosphole, 1,1-dichloro- 2,3,4,5-tetraethylgermole reacts with two equivalents of the maleic derivatives to 1,4,7,8-tetraethylbicyclo[2.2.2] oct-7-ene-2,3,5,6-tetracarboxylic acid anhydride ( 3) as well as the aza-analogue 4. The molecular structure of 3 shows the formation of an exo, exo-product. The 1,1-dichloro- 2,5-bis( trimethylsilyl)-3,4-diorganylgermoles with R = Me ( 5), nPr ( 6) and Ph ( 7) show no reactivity toward maleic acid derivatives.