Carboxylic acids, from acyl dianions

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

A complementary access to alkoxy- and aminocarbene complexes ( Semmelhack-Hegedus route ) involves the addition of the pentacarbonylchromate dianion 18 (obtained from the reduction of hexacarbonylchromium with C8K) to carboxylic acid chlorides and amides [27] (Scheme 10). While alkylation of acyl chromate 19 leads to alkoxycarbene complexes 12, addition of chromate dianion 18 to carboxylic amides generates the tetrahedral intermediates 20, which are deoxygenated by trimethylsilyl chloride to give amino carbene complexes 14. 

Intramolecular acylation of alkylsilanes. Cyclopentanones can be prepared by ring closure of 5-(trimethylsilyl)alkanoyl chlorides mediated by AlCl,. The starting materials are readily available from alkylation of the dianion of a carboxylic acid with a 3-(trimethylsilyl)alkyl bromide or iodide (equation 1). 

C-Acylation. C-Acylation can be realized by treatment of acylimidazoles, derived from carboxylic acids and 1, with the magnesium salts of malonic esters prepared by using Bu2Mg. Acyl imidazoles can also undergo Claisen-type condensation with the dianion of -keto esters (eq 38). ... 

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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