Results Synthetic Organic Ligands

14 (one ter-butyl group on each cyclohexyl ring mixture of stereoisomers) 

The synthetic methods used followed one of the following paths  

Higher yields are obtained when the reaction rate is increased by using dipolar aprotic solvents, with the possible operation of a template effect (77) of a precomplexed cation (64). Again, this shows that high dilution techniques are not necessary in many cases, but they would certainly increase the yields. Synthesis of polyether-sulfides are generally facilitated by the greater reactivity of — S compared to — O- in nucleophilic displacement reactions. However, the yield is low when path b) is followed (74). 

Chiral macrocyclic amino-ethers have been prepared recently (69). Ligands of type E are obtained by attaching a chain (or two chains, one at each Z center to the type D macrocycles (81). The synthesis of macro-cyclic peptides will not be discussed here. 

Macrobicyclic ligands of type G containing 0, N (28,67,82) 0, N, S or N, S (76) heteroatoms, with O, S in the bridges and with nitrogen bridge- 

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In traditional synthetic organic chemistry, the Wittig reaction plays an important role in carbon-carbon bond extension from the carbonyl group. CM is an attractive alternative for carbon-carbon extension from a terminal alkene. In fact, a pyrroh-dine ring of anthramycin derivative 55 has been constructed by RCM of 52, and the sidechain has been extended by CM of terminal alkene of 54 with ethyl acrylate. " In the CM, ruthenium carbene complex Ij, reported by Blechert, gives a good result since the ligand of the catalyst easily dissociated from the ruthenium metal at room temperature ... 

This chapter illustrates that electron-rich transition metal-diene complexes can couple with carbon electrophiles and, thereby, provide unusual methods for carbon-carbon bond formation. These procedures are of interest from a synthetic viewpoint since normally uncomplexed dienes or polyenes are not reactive toward weak carbon electrophiles or, with strong electrophiles, undesirable reactions such as polymerization occur. Furthermore, the metal-mediated route often results in desirable regio- and/or stereo-selectivity. Important to the utility of these methods is the ability to free the organic ligand from the metal. In most instances efficient oxidative procedures have been developed for such cleavage reactions. 

Although the observed effect of the metal ions on the extent of O-benzoy-lation or C-benzoylation is important for synthetic purposes, it is questionable whether any conclusions of significance to the reactions of chelated organic ligands can be obtained from these results. It would be of great interest to repeat these reactions with the inert chelates of Rh(III), Co (III), Al(III), and Cr(III). 

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