Organometallic compounds conjugate additions

In Grignard reactions, Mg(0) metal reacts with organic halides of. sp carbons (alkyl halides) more easily than halides of sp carbons (aryl and alkenyl halides). On the other hand. Pd(0) complexes react more easily with halides of carbons. In other words, alkenyl and aryl halides undergo facile oxidative additions to Pd(0) to form complexes 1 which have a Pd—C tr-bond as an initial step. Then mainly two transformations of these intermediate complexes are possible insertion and transmetallation. Unsaturated compounds such as alkenes. conjugated dienes, alkynes, and CO insert into the Pd—C bond. The final step of the reactions is reductive elimination or elimination of /J-hydro-gen. At the same time, the Pd(0) catalytic species is regenerated to start a new catalytic cycle. The transmetallation takes place with organometallic compounds of Li, Mg, Zn, B, Al, Sn, Si, Hg, etc., and the reaction terminates by reductive elimination. 

In addition to the asymmetric conjugate addition involving an enone substrate and a relatively inactive nucleophile, there exists another kind of reaction in which a deactivated substrate and a normal nucleophile are involved. For example, under proper conditions, ordinary organometallic compounds such as... 

The conjugate addition of organometallic reagents to a./i-unsaturated compounds is one of the basic methods in our repertoire for the construction of carbon-carbon bonds. These addition reactions have been used as key steps in the synthesis of numerous biologically active compounds, and show a broad scope due to the large variety of donor and acceptor compounds that can be employed. It is evident that a tremendous effort has been devoted over the last three decades to develop asymmetric variants of this reaction. ... 

Enantlomerically pure B-suhstituted carbonyl compounds serve as useful intermediates in the synthesis of many chiral organic compounds. The enantloselective synthesis of acyclic 0-substituted carboxylic acids has been reported by Meyers, Mukaiyama, and Koga. However, no effective, general method for the enantio-controlled preparation of P-substituted cycloalkanones was available prior to the investigations by the submitters. For example, poor enantloselectivity was observed in conjugate additions of organometallic... 

The first results of anionic polymerization (the polymerization of 1,3-butadiene and isoprene induced by sodium and potassium) appeared in the literature in the early twentieth century.168,169 It was not until the pioneering work of Ziegler170 and Szwarc,171 however, that the real nature of the reaction was understood. Styrene derivatives and conjugated dienes are the most suitable unsaturated hydrocarbons for anionic polymerization. They are sufficiently electrophilic toward carbanionic centers and able to form stable carbanions on initiation. Simple alkenes (ethylene, propylene) do not undergo anionic polymerization and form only oligomers. Initiation is achieved by nucleophilic addition of organometallic compounds or via electron transfer reactions. Hydrocarbons (cylohexane, benzene) and ethers (diethyl ether, THF) are usually applied as the solvent in anionic polymerizations. 

Most main group organometallic compounds undergo nucleophilic reactions with carbonyl groups, whereas 1,4-conjugate addition to enones... 

There are many addition reactions of a,(3-unsaturated aldehydes, ketones, and related compounds that are the same as the carbonyl addition reactions described previously. Others are quite different and result in addition to the alkene double bond. Organometallic compounds are examples of nucleophilic reagents that can add to either the alkene or the carbonyl bonds of conjugated ketones (see Section 14-12D). Hydrogen cyanide behaves likewise and adds to the carbon-carbon double bond of 3-butene-2-one, but to the carbonyl group of 2-butenal ... 

Chiral Metal Atoms in Optically Active Organo-Transition-Metal Compounds, 18, 151 13C NMR Chemical Shifts and Coupling Constants of Organometallic Compounds, 12, 135 Compounds Derived from Alkynes and Carbonyl Complexes of Cobalt, 12, 323 Conjugate Addition of Grignard Reagents to Aromatic Systems, I, 221 Coordination of Unsaturated Molecules to Transition Metals, 14, 33 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365... 

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