Cyclopropenes fused

Rate-strain relationship studies show 1,2-diphenylcyclopropene to undergo epoxi-dation more slowly than expected. The relative rate of epoxidation of cyclopropenes fused to cycloheptane 19 revealed moderate backside interaction of the alllylic cyclopropene substituents (Eq. 10). ... 

When an alkynylsilyl group is present at the a-position of zirconacycles such as zircona-cyclopropene, zirconacyclopentene, or zirconacyclopentadiene, an unusual rearrangement proceeds to give zirconacyclosilacyclobutene derivatives 132, as shown in Eq. 2.78 [57]. The zirconacyclosilacyclobutene fused complex 132 and the zirconacydohexadiene silacy-clobutene fused complex 137 have been characterized by X-ray analysis. 

Addition of a rhodium carbenoid to an alkyne leads to a cyclopropene derivative. In an intramolecular context, the fused cyclopropene moiety is unstable and undergoes ring opening to generate a rhodium vinyl carbenoid entity, which can then undergo cyclopropanation or cyclopropena-tion, carbon hydrogen insertion, and ylide generation. This is illustrated... 

One major drawback of the cycloaddition approach to cycloproparenes is the low reactivity of 1,2-dihalocyclopropenes towards unsubstituted or monosubstituted buta-1,3-dienes which occur preferably in the s-trans conformation. Owing to the low thermal stability of the cyclopropenes, long reaction times are often required, and the yields of cycloadducts are low. These difficulties may be overcome if the required 1,6-dihalobicyclo[4.1.0]hept-3-ene precursor is constructed from a cycloprop-l-ene-l,2-dicarboxylate. The cycloadditions are carried out at 25-40 C in high yield. Hydrolysis and halodecarboxylation of the adduct produces the cyclo-proparene precursor, albeit in disappointing yield. Nevertheless, the approach was used for the first preparation of a cyclopropa-fused tropone 16. ... 

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