Diorganozinc oxidation

Properties of zinc salts of inorganic and organic salts are Hsted in Table 1 with other commercially important zinc chemicals. In the dithiocarbamates, 2-mercaptobenzothiazole, and formaldehyde sulfoxylate, zinc is covalendy bound to sulfur. In compounds such as the oxide, borate, and sihcate, the covalent bonds with oxygen are very stable. Zinc—carbon bonds occur in diorganozinc compounds, eg, diethjizinc [557-20-0]. Such compounds were much used in organic synthesis prior to the development of the more convenient Grignard route (see Grignard reactions). 

The oxidation of organozinc halides and diorganozincs is a facile radical reaction.1 It provides usually a mixture of hydroperoxides and alcohols,12 13 but through careful control of the reaction conditions it allows preparation of either new hydroperoxides or by working under reductive conditions solely alcohols.14,15 Thus, the treatment of myrtanylzinc bromide with oxygen in perfluorohexanes12,13 at -78 °C affords the desired hydroperoxide with high selectivity. This method is well suited for the preparation of polyfunctional hydroperoxides (Scheme 9.6). 

A study of palladium-catalysed conjugate addition of diorganozincs to various enone types indicated that both Pd(0) and Pd(II) complexes could catalyse the reaction. Phosphine ligands such as PPhj or PBuj were effective, but only at a 1 1 Pd P ratio a 1 2 ratio caused yields to collapse. The observation is consistent with a mechanism computed for the Pd(0) case, in which the enone is simultaneously coordinated to Pd(0) and R2Zn this undergoes oxidative addition to palladium with simultaneous transmetalation from Zn to Pd, followed by reductive elimination. 

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