Rearrangements of bridged diallenes. A facile synthesis of novel condensed heterocycles by tandem [3,3]-sigmatropic rearrangement and double intramolecular michael addition of diallenyl disulfides and diselenides. Isolation of stable diallenyl diselenides

Thienothiophene 14 and selenoloselenophene 16 have been synthesized by the action of lithium methoxide on τ,τ-dimethylallenyl thiocyanate and selenocyanate, respectively. A multistep mechanism involving bis-τ,τ-dimethylallenyl disulfide (20) or diselenide as key intermediates, is suggested. The latter are believed to undergo consecutive 3,3]-sigmatropic rearrangement and double Michael addition, to the observed products. This mechanism is supported by the isolation of bis-τ,τ- diisopropylallenyl and bis-τ-methyl-τ-isopropylallenyl diselenides, under the same reaction conditions, and the rearrangement of the latter to the expected selenoloseleophene 33. The synthesis of the novel mixed selenolothiophene 35 by treatment of a mixture of allenyl thiocyanate 13 and selenocyanate 15 with lithium methoxide, is also described.