Catalytic and Stoichiometric Reactions of Allylic Compounds

7t-Allyl complexes are prepared from various allylic compounds, conjugated dienes and alkenes. Oxidative addition of various allylic halides and esters to low-valent metal complexes provides a general synthetic method for 7r-allyl complexes [1], Some of them can be isolated. Both electrophilic and nucleophilic 7t-allyl complexes are known. These 7r-allyl complexes react with either nucleophiles or electrophiles depending on metal species, and offer useful synthetic methods. Some bis-7t-allyl complexes 1 are known to show amphiphilicity. 

Both stoichiometric and catalytic reactions of allylic compounds via 7r-allyl complexes are known. Reactions of nucleophilic 71-allyl complexes with electrophiles involve oxidation of metals and hence constitutes stoichiometric reactions. 7i-Allyl complexes of Ni, Fe, Mo, Co and others are nucleophilic and undergo the stoichiometric reaction with electrophiles. However, electrophilic 71-allyl complexes react with nucleophiles, accompanying reduction of metals. For example, 71-allylnickel chloride (2) reacts with electrophiles such as aldehydes, generating Ni(II), and hence the reaction is stoichiometric. In contrast, electrophilic 7i-allylpalladium chloride (3) reacts with nucleophiles such as malonate and Pd(0) is generated. Thus repeated oxidative addition of allylic compounds to Pd(0) constitutes a catalytic reaction. 

Some metals are amphiphilic, reacting with both electrophiles and nucleophiles. For example, the Ru complex 4 reacts with both aldehyde as the electrophile and malonate as the nucleophile under different conditions [2], 

Among 7i-allyl complexes of several transition metals, the chemistry of n-allylpalladium has been studied most extensively. From the standpoint of organic synthesis, reactions involving 7i-allylpalladium complexes are by far the most important therefore, their synthetic applications are mainly treated in this chapter. 

The reaction of 7i-allylpalladium chloride (3) with carbon nucleophiles such as malonate, acetoacetate and enamines was discovered in 1965 [3]. This reaction constitutes the basis of stoichiometric as well as catalytic 7i-allylpalladium chemistry. 

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