Methylenecyclopentanes specials

In addition to the above discussed transition metal catalyzed [3+2]-eycloadditions some other methylenecyclopentane syntheses have been developed which are of special interest within the context of annelation procedures. 

Starting from a methylenecyclopropane, the two step sequence — catalyzed codimerization to a methylenecyclopentane and subsequent oxidation of the exomethylene group — is often much more convenient for the preparation of specially substituted cyelopentanones than hitherto known procedures. 3-Oxocyclopentane methylcarboxylate, for example, has been prepared in four steps starting with di-methylmalonate and dimethylitaconate (overall yield 18%)234), the new two step procedure furnishes this compound in an overall yield of 83 %. 

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