Carbon-metal bonds, oxidations, copper© acetate

Organomagnesiums frequently prove superior also in other types of reactions. They may facilitate the oxidation of a carbon-metal to a carbon-oxygen bond, secure clean monoaddition of an acetylide to an activated ester (a critical issue in a monensin synthesis X favor in the presence of a copper catalyst 1,4-addition onto a conjugated enone over 1,2-addition, reorient the attack of formaldehyde on a benzylic entitiy from the a- to the or /to-position, and provide diastereoselectivity in nucleophilic additions onto aldehydes. Furthermore organomagnesiums combine under carbon-carbon linking with a variety of organic halides, tosylates, and acetates if the process is mediated by transition elements such as palladium(O) copper(I), nickel(II) or iron(II) Organoalkalis are often less fit to enter such catalytic cycles. 

Ruthenium- and rhodium-catalytic systems for the direct cross-dehydrogenative coupling (CDC) of acrylamides with electron-deficient alkenes forming (Z, )-dienamides using copper(II) acetate as the oxidant has been developed. Both methods exhibit wide functional group compatibility and substrate flexibility. It is proposed that the reaction is initiated by cyclometalation of acrylamide by amide-directing C-H bond activation. Coordination of the alkene to the metal centre, followed by insertion of the carbon-carbon double bond, forms a seven-membered ruthacycle or rhodacycle species. Subsequent -elimination occurs to afford the desired (Z, )-dienamide. A CDC between two heteroarenes is effected with copper(II) acetate in the absence... 

The less highly substituted bond of a siloxycyclopropane is quantitatively opened by mercury(II) acetate to afford -mercurio ketones. In the same pot these are transformed to a-methylene ketones in virtually quantitative yield on treatment with one equivalent of palladium(II) chloride in the presence of lithium chloride and lithium carbonate (2 equiv each). Catalytic amounts of palladium(II) chloride (0.1 equiv) are sufficient in the second step, if two equivalents of copper(II) chloride is added as an oxidant. Mechanistically, the second step involves trans-metalation to a j -palladio ketone followed by /i-hydride elimination. In bicyclic systems it is sometimes necessary to add triethylamine to avoid HPdCl induced double-bond shifts in the reaction product. Examples are the rearrangements of 18, 20 and 22. ... 

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