Carboxylic acids coupling with allylic acetates

The relatively weak leaving group (acetate) is lost from the allylic acetate with Lewis acid catalysis to give a stable allyl cation. This couples with the other (isopentenyl) acetate in a way very similar to the natural process. However, what happens to the resulting cation is not well controlled. Loss of each of the three marked protons gives a different product. In the enzymatic reaction, loss of the proton would probably be concerted with C-C bond formation as a basic group, such as an imidazole of histidine or a carboxylate anion, would be in the right position to remove one of the protons selectively. 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

---