Reactions Using Organometallic Reagents

The reactions of organometallic reagents with chlorocyclophospha-zenes are quite complex and depend on several variables, such as (a) the ring size of the cyclophosphazene, (b) the nature of the organometallic reagent, and (c) the reaction conditions including the type of solvent used, the temperature of the reaction, etc. (10). 

The use of chiral chelating agents in reactions of organometallic reagents with carbonyl compounds has been intensively investigated (134-138). However, the influence of such chiral addends in the aldol process has not met with much success. In the presence of the... 

A couple of further useful reactions, involving organometallic reagents, have been developed—mainly by Kocienski and coworkers—for converting 4-hydroxy-1-alkenyl carbamates into various alkenes (equation 104) °- p j. j-gaction type, only one example is depicted. 

The carbonylmetallate anions are extremely useful organometallic reagents, particularly for the syntheses of heteropolymetallic clusters.3,4,7 However, they have rarely been isolated in the solid state and their solutions are obtained either by reduction of their dimers or by reaction of NaCsHs with the parent metal carbonyls,2 and immediately used. The first method is not very economical since the dimers are usually themselves obtained from the metallate anions. The second method has been improved as detailed below to allow the easy isolation of the pure Na[M(CO)3(//s-CsH5)] (M = Cr, Mo, W) solids as DME solvates.4 The nonsolvated Na[M(CO)3(f/5-C5H5)] salts can... 

Rapid development of this area followed the discovery of routes to these complexes, either by ready conversion of terminal alkynes to vinylidene complexes in reactions with manganese, rhenium, and the iron-group metal complexes (11-14) or by protonation or alkylation of some metal Recent work has demonstrated the importance of vinylidene complexes in the metabolism of some chlorinated hydrocarbons (DDT) using iron porphyrin-based enzymes (15). Interconversions of alkyne and vinylidene ligands occur readily on multimetal centers. Several reactions involving organometallic reagents may proceed via intermediate vinylidene complexes. 

Pyrylium behaves as the synthetic equivalent of the pentadienal cation in its reactions with organometallic reagents, allowing the stereoelective formation of 2Z,4 -dienals. This approach to the synthesis of retinoids using a variety of pyrylium salts has been most successful (95JCS(P1)2385). 

Aromatic Substitutions Using Organometallic Reagents 790 17-14 Addition Reactions of Benzene Derivatives 796 Mechanism 17-9 The Birch Reduction 797 17-15 Side-Chain Reactions of Benzene Derivatives 798... 

To make ethers more reactive, they must be complexed with strong Lewis acids. BF3 is commonly used with cyclic ethers, and even with epoxides it increases the rate and yield of the reaction when organometallic reagents are used as nucleophiles. BF3 is most easily handled as its complex with diethyl ether, written BF3 OEt, BuLi does not react with oxetane, for example, unless a Lewis acid, such as BF3, is added, when it opens the fouremembered ring to give a quantitative yield of H-heptanoI. 

The use of aminosulfites in the synthesis of o.p. sulfoxides was described for the first time in 1973 by Wudl and Lee,98 using ephedrine as chiral auxiliary. In 1991, Benson and Snyder reported a modification of the Wudl and Lee procedure, obtaining o.p. sulfoxides in high yield by sequential displacement reactions of organometallic reagents on the 1,2,3-oxathiazolidine-S-oxide (aminosulfite 70), obtained from ephedrine and thionyl chloride.99... 

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