Cyclopropanes via nucleophilic attack at the central carbon of (π-allyl)palladium complexes

Synthesis of Cyclopropanes by Intramolecular Attack ofN-Nucleophiles on the Central Carbon of (π-Allyl)palladium Complexes

“…The central attack can either occur with the lone pair of the neutral secondary amide, as the reaction is also observed when the base K 2 CO 3 is substituted by sodium azide,20 or with the amide anion, as the acidity of nitrogen‐bound protons is assumed to increase in the coordination sphere of palladium complexes 21. The formation of the cyclopropane moiety is probably facilitated by conjugation of the e A Walsh orbital of the cyclopropane with a π‐orbital of the adjacent aryl group, as the plane of the three‐membered ring in 3a is almost parallel to its axis22 (which may also explain the “aryl effect” described by Hoffmann11). An enabling feature is the kinetically favoured formation of a five‐membered ring rather than the six‐membered ring 4a which results from terminal substitution.…”

Development of Palladium-Catalyzed Decarboxylative Allylation of Electron-Deficient Sulfones and Identification of Unusual Side Products

“…There are a few examples of cyclopropyl products from allylation-type processes. Hegedus reported in 1980 that ester enolates attacked the central carbon of (π-allyl)palladium complexes in THF/HMPA/Et 3 N to give excellent yields of cyclopropane products and Hoffmann reported on the formation of cyclopropanes via attack on the central carbon of (π-allyl)palladium complexes by a variety of stabilized nucleophiles in the mid-1990s. − Satake reported the cyclopropylation of silyl ketene acetals by allyl acetate using an allylpalladium–pyridinylpyrazole complex. The allylation product was competitive.…”

Recent Advances in Synthesis of Cyclopropanes

“…The attack, however, may be directed to the central carbon atom of the π-allyl group to produce cyclopropyl derivatives by appropriate choice of nucleophile, metal ligand and reaction conditions (equation 33). A variety of nucleophiles (pK a 20)including ester and ketone enolates and α-sulfonyl carbanions (33) react with dimeric (π-allyl)palladium chloride in the presence of TMEDA under carbon monoxide atmosphere to give the corresponding α-cyclopropyl derivatives in good yields (equation 34) 50,51 . The nature of the counterion of the nucleophile plays an important role and the yield of cyclopropanes appears to increase when the nucleophile becomes more (34) ionic, i.e.Nu − K + is preferred to Nu − Li + .…”