Palladium cyclopropenones

Cyclopentenes Benzy chlorobis(triphenyl-phosphine)palladium( lI). Cyclopropenone 1,3-propanediyl ketall. Di-p,-carbonylhexa-carbonyldicobalt. 

Cyclopentenes Benzylchlorobis(triphenyl-phosphine)palladium(II). Cyclopropenone 1,3-propanediyl ketal. Di- x-carbonylhexa-carbonyldicobalt. 

The non-hydrocarbon substrates most often employed in dimerization or oligomerization reactions are cyclopropenone acetals, due to their ease of preparation. 3,3-Dimethoxycyclo-propene has been treated with various palladium(O) complexes. In the absence of phosphane, bis(dibenzylideneacetone)palladium leads to cyclodimerization, with 3,3,6,6-tetramethoxy-exu-tricyclo[3.1.0.0 ]hexane (30) being formed in 74 /o yield. No cyclotetramers, as in the reaction of 3,3-dialkyl- or 3,3-diarylcyclopropenes, are formed. ... 

Addition of zinc(II) chloride to the lithium compound 4 gave the zinc derivative 6, which is stable even at 50 °C in tetrahydrofuran. The palladium-catalyzed coupling reaction of the zinc salt with vinyl iodides, vinyl triflates and aryl iodides produced vinyl and aryl derivatives 7 and 8 (Table 1, entries 11-16). Cerium derivatives of cyclopropenone acetals were prepared by addition of the lithium salt 4 to a suspension of anhydrous cerium(III) chloride in tetrahydrofuran at — 70 C. The resulting organocerium reagent coupled with oc-aminoaldehydes (Table 1, entry 17). ° ... 

Examples are provided by the catalytic reduction of diphenyl- [26], di-n-propyl- [88], di-t-butyl- [111] andn-pentyl- [100] cyclopropenones. However, when palladium replaced platinum as catalyst, the product from di-n-propylcyclopropenone was instead 2-propylhex-2-enal [88]. 

Annulation between cyclopropenone acetals and the electron-deficient alkyne 130 proceeded in the presence of a palladium catalyst to give cyclopenta-dienone acetals in good yields (Scheme 2.97) [151]. The reaction can also occur thermally. 

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