Dianions y-acylation

They are made by y-acylation of 1,3-diketones with carboxylic esters by means of KNH2 via dianions 9. Their cyclization to give 4//-pyran-4-ones is brought about by strong acids ... 

Ryu, I. Ikebe, M. Sonoda, N. Yamato, S.-Y. Yamamura, G.-H. Komatsu, M. Chemistry of ketone a,/ -dianions. Acylation reactions of dianion cuprates by acid chlorides. Tetrahedron Lett. 2002, 43, 1257-1259. 

While the majority of examples of substrate control deal with cyclic sterocontrol, there are a few examples where diasteroselectivity is induced in an acylic system.27 A notable example of this was demonstrated during the synthesis of a fragment of tubulysin, by Wipf and co-workers.28 Utilizing a Davis reagent in their synthesis of an a-hydroxy-y-amino acid, the enolate of the y-amino acid derivative 42 was reacted with 1 to form the a-hydroxy derivative 43 as a single diastereomer in good yield. The stereoselective reaction has precedence in literature and likely involves a highly chelated dianionic species.29... 

Another precursor for DALA is succinoyl chloride monomethyl ester that can undergo chain extension in the presence of hippuric acid and a base catalyst such as Y-picoline (Figure 5) (22). The initial reaction involves acylation of the dianion of hippuric acid. The resulting oxazolinone 9 can be hydrolyzed in aqueous hydrochloric acid to yield DALA. In a similar manner, succinic anhydride can serve as acylating agent when it is treated with the dianion of ethyl hippurate (23). 

A completely different approach to Y-keto-esters proceeds via Michael additions of carboxylic acid dianions to an a-anilino-acrylonitrile followed by alkylation of the resulting anion and finally acidic hydrolysis (Scheme 13). Overall yields are in the range 47-79% the method is also useful in the synthesis of r-keto-amides. An alternative anion-based route to y-keto-esters utilizes the homoenolate (166) as the interroediate which undergoes smooth acylation by a wide variety of acid chlorides.The homoenolate is obtained from the corresponding iodoester using Zn-Cu couple, and it seems likely that the method can be used to prepare more highly substituted keto-esters although such reactions have not yet been reported. 

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