Vinylcyclopropanes ring-opening polymerization

Suzuki has shown that vinylcyclopropane 143 behaves both as an electrophile and a nucleophile and thus undergoes palladium-catalyzed ring-opening polymerization as shown in Equation (66). Vinyl cyclopropane 143 first reacts with palladium(O) to induce ring opening of the cyclopropane ring and forms zwitterionic TT-allylpalladium/molonate anion species. Repeated intermolecular attack of the malonate anionic moiety to the 7r-allylpalladium part through bond formation of an r/i -carbon atom affords finally the polymer 142. ... 

Figure 4. Radical ring-opening polymerization of vinylcyclopropane derivatives.

Figure 6. (A) Radical ring-opening polymerization of vinylcyclopropane with trimethylsiloxy groups and acidic hydrolysis of the poly(silyl enol ether)s. (B) Macromolecular reaction of the poly(silyl enol ether) with electrophile.

Reviews on radical ring-opening polymerization include those by Sanda and Endo, " Klemm and Schultz, Cho, " Moszner e( Endo and Yokozawa Stansbury and Bailey. A review by Colombani on addition-fragmentation processes is also relevant. Monomers used in ring-opening are typically vinyl (e.g. vinylcyclopropane - Scheme 4.20 Section 4.4.2.1) or methylene substituted cyclic compounds (e.g. kctenc acetals - Section 4.4.2.2) where addition to the double bond is followed by p-scis.sion. 

The complete ring-opening nature of the polymerization of a vinylcyclopropane stimulated us to apply it to radical ring-opening polyaddition... 

Styrene is reported to undergo reduction upon treatment with trifluoroacetic acid and triethylsilane,203 although competing polymerization reactions limit the yield of ethylbenzene to only 30% (Eq. 63).70 Vinylcyclopropane is reduced to ethylcy-clopropane within 30 minutes under similar conditions (Eq. 64) 232 It is important to note that the cyclopropane ring of ethylcyclopropane can be opened under these reaction conditions, albeit with longer reaction times, to give some trans-2-pentene in the final reaction mixture.233... 

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