Unsaturated carboxylic acids, lithium salts

Lithium salts of dianions of unsaturated carboxylic acids can adopt the structure of lithium dienolates, 3 or 4 (equation 3), or lithium salts of oxycarbonyl substituted allyl anions, 5 or 6 (equation 4). In any case these formulations provide an oversimplified view of the structures, as these dianions are expected to form ion pairs and aggregates in weakly polar solvents such as diethyl ether or thf. ... 

Hunsdiecker Reactions. The Hunsdiecker reaction is the de-carboxylative halogenation of metal carhoxylate salts. The reaction of a,/3-unsaturated carboxylic acids with NCS and catalytic lithium acetate in acetonitrile-water provides the corresponding /3-halostyrenes in moderate yields under mild conditions. The reaction proceeds with a good degree of stereospecificity. For example, the reaction of 3-(4-methoxy-phenyl)-acrylic acid with NCS with a catalytic amount of lithium acetate at room temperature provides l-(2-chloro-vinyl)-4-methoxybenzene in good yield (eq 23). 3... 

The 14,15-double bond present in tabersonine was introduced into the /3-ethyl isomer of lactam 491 by treatment with LDA-diphenyl disulfide followed by oxidation and elimination to give the a,fl-unsaturated lactam 492. Murphy s law operated at this point, for upon lithium aluminum hydride reduction, 492 gave only a 5% yield of the amino alcohol 493. An alternative procedure was therefore developed. Hydrolysis gave a carboxylic acid, and treatment with ethyl chloroformate and triethylamine followed by sodium borohydride in aqueous THF gave a lactam alcohol 494, which after silylation was reduced with lithium aluminum hydride to amino alcohol 493 in 58% overall yield from 492. Mesylation and elimination of HC1 in refluxing chloroform gave the unsaturated mesylate salt 482. The same salt was prepared previously by Ziegler and Bennett... 

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