Zinc, organo- reagents preparation

The zinc organo-lialide is prepared for use by heating together the zinc-copper couple, the alkyl or aiyl halide, ethyl acetate, and toluene for about an hour, the reaction being started if necessary with a ciystal of iodine. All the reagents must be well dried, and the colomdess viscous liquid which results is ntilised by adding to it the acid chloride dissolved in toluene, and when the required amount has been added the intermediate zinc complex is decomposed by the addition of dilute sulphuric acid.1... 

Support-bound transition metal complexes have mainly been prepared as insoluble catalysts. Table 4.1 lists representative examples of such polymer-bound complexes. Polystyrene-bound molybdenum carbonyl complexes have been prepared for the study of ligand substitution reactions and oxidative eliminations [51], Moreover, well-defined molybdenum, rhodium, and iridium phosphine complexes have been prepared on copolymers of PEG and silica [52]. Several reviews have covered the preparation and application of support-bound reagents, including transition metal complexes [53-59]. Examples of the preparation and uses of organomercury and organo-zinc compounds are discussed in Section 4.1. 

There are many examples of asymmetric addition of organo-metallic reagents to aldehydes (chapter 27) and the one that works here uses Seebach s TADDOL 51 as a ligand for zinc.8 The TAD-DOL 51 is prepared from tartaric acid and used as its titanium (IV) complex to catalyse the addition of the organozinc compound to acrolein. After photochemical cyclisation in the presence of Cu(I), the bicyclic alcohol 53 was isolated in good yield and >98% ee. 

Catalytic, enantioselective Michael reactions of cyclopentenones have attracted particular attention in recent years. Ben L. Feringa, Albert S. C. Chan, Andreas Pfaltz and Amir H. Hoveyda described various hgand systems for stereoselective addition of organo-zinc reagents to cyclopentenones. With the aid of a phos-phoramidite derived from BINOL, Feringa developed an enantioselective, catalytic domino-Michael/aldol reaction for the preparation of (+)-PGEi methyl ester. [223]... 

It is expected that endothermic or weakly exothermic organometallic compounds will be the most versatile reagents RM in such reactions. Such compounds are found among the heavy B elements (Hg, Tl, Pb and Bi). Of these the air-stable and readily prepared (though toxic) organo-mercury compounds are the most widely used. Let us consider the heats of reaction between dimethyl mercury and zinc and cadmium ... 

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