Abstract (Diazomethyl)diphenylphosphine oxide (2a) adds onto the 1-cyclopropene phosphonates 1a and c under formation of the 2.3-diazabicyclo[3.1.0]hex-2-enes 3a and c. 3a is easily converted into the 1.4-dihydropyridazine 5a. On the other hand the reaction of 1b with 2a directly affords the 1.4-dihydropyridazine 5b. The 2.3-diazabicyclo[3.1.0]hex-2-enes 3a and c isomerize to the allyl diazomethanes 4a and c on heating in benzene. In the case of the reactions 2b+1b as well as 6+1a the direct formation of allyl diazo compounds (4d and 8a respectively) is observed. In a novel reaction 9-diazofluorene (6) yields the 1.3-butadiene 9 when reacted with the cyclo-propene 1b.
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