Enolate complexes synthesis

Arene ruthenium complexes are used frequently in metal-mediated organic synthesis for a wide range of reactions.5 For the purposes of our studies we have focused attention mainly on enol formate synthesis as a representative reaction for comparing the activity of 2 with its non-supported analogue 5. As with the supported cobalt complex, we find that attachment of 5 to a polymer support has little effect in its catalytic activity with a range of enol formates being prepared in high yield. 

This cyclization has obvious applications to the synthesis of steroids and indeed Johnson et al. applied this reaction to a synthesis of dZ-progcsterone. The key step in the synthesis involves the cyclization of (3) to give (4). This reaction was carried out with trifluoroacetic acid as above, but ethylene carbonate was added to the reaction to trap the vinyl cation. After cyclization potassium carbonate was added to hydrolyze the enol complex. In this way (3) was converted into (4) in 71 % yield. The tetracyclic ketone (4) was converted into progesterone (6) by ozonization followed by intramolecular aldol condensation. Nole that (4) is a 5 1 mixture of the 17/7- and 17a-epimeric ketones. The mixture was converted into (6) and then separated by fractional crystallization. 

In addition, the synthesis of enolate complexes of nickel has been carried out by Campora and co-workers <2003CC1742, 2003JA1482>. Treatment of a THF solution of Ni(C6H4-o-C(0)CH3(Gl)(dippe) 106 with 1 equiv of KO/-Bu allowed the preparation of the nickel enolate 107 in good isolated yield (60%). O-Coordination of the enolate fragment could be proposed on the basis of the NMR spectra. Thus, the terminal methylene group gave rise... 

Davies examined the same reaction.He found that when using an excess of Et2Al adducts of the enolate, the diastereoselectivity ratio became > 100 1. Further, if Cu(I) was used as counter ion the opposite stereochemistry was obtained.Moreover both Davies and Liebsekind used this chiral iron auxiliary in a stereoselective synthesis of S-lactams. " " Liebeskind reported that chiral iron enolate complex condensed with imines in the presence of Et2Al counter ion to give two isomers with a ratio up to 20 1. Oxidation with I2/R3N produced the racemic jS-lacatms (Scheme 3.9)... 

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