Aspects of Homogeneous Catalysis

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1. INTRODUCTION Although quite spectacular results have been obtained in the last few decades in the field of homogeneous transition metal catalyzed transformations of olefins and alkynes [1], reactions which could lead to heterocycles have been partly neglected. An obvious reason for this is that substrates containing heteroatoms such as N, 0 or S could coordinate the metal and suppress the catalytic activity. Nevertheless, some interesting early examples of transition-metal-catalyzed syntheses of heterocyclic compounds have been reported and these have been reviewed by C. W. Bird [2] . More recently the incorporation of CO , which enables esters and lactones 2 to be synthesized from olefinic starting materials, has begun to attract attention (see, for example, ref. [3]). The dominant role of palladium as the catalyst for the formation of O-containing heterocycles has been suggested to be associated with the relatively low strength of the Pd-O bond. Among the first examples of a nitrogen-containing heterocycle to be formed by homogeneous catalysis is the triazine shown in Equation 1 which is the product of the trimerization of benzonitrile in the presence of iron penta carbonyl or Raney­ nickel [4] .