Ethylene derivatives Allyl..., Double bond

The two double bonds in 2,3-dimethoxycarbonyInorbomadiene are almost equally active. Furthermore, the reactions with methylenecyclopropane are stereoselective leading exclusively to the exo-isomers. Both observations are in striking contrast to the results obtained in the Pd(0) catalyzed cycloadditions of 2-[(tri-methylsilyl)methyl]allyl acetate with norbornadiene derivatives The last observations automatically lead to the conclusion that non-activated alkenes also could undergo these reactions. Indeed it was found that ethylene, norbornene, norbornadiene and allene react with methylenecyclopropane to give cycloadducts (Scheme 7). The reason for the limitation to these alkenes lies in the ability of methylenecyclopropane to compete successfully with alkenes in n-complexation to the metal. Thus cyclodimerization of methylenecyclopropane is much faster than codimerization with other alkenes, which give less stable rt-com-plexes with Pd(0). 

One distinguishes palladium(0)- and palladium(ll)-catalysed reactions. The most common palladium(O) transformations are the Mizoroki-Heck and the cross-coupling transformations such as the Suzuki-Miyaura, the Stille and the Sonogashira reactions, which allow the arylation or alkenylation of C=C double bonds, boronic acid derivates, stan-nanes and alkynes respectively [2]. Another important palladium(O) transformation is the nucleophilic substitution of usually allylic acetates or carbonates known as the Tsuji-Trost reaction [3]. The most versatile palladium(ll)-catalysed transformation is the Wacker oxidation, which is industrially used for the synthesis of acetaldehyde from ethylene [4]. It should be noted that many of these palladium-catalysed transformations can also be performed in an enantioselective way [5]. 

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