Double bonds, organometallic addition

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 ... 

House investigated the role of cuprous ions in the conjugate addition of organometallic reagents. He found that the catalytic effect can be explained by the intervention of a methyl copper derivative, which reacts rapidly with the carbon-carbon double bonds of the conjugated system. 

The addition of organometallic reagents to the C —N double bond of imines 1 provides an attractive route to amines 21 2. However, due to the poor electrophilici ty of imines, this method is often plagued by competitive reactions ... 

Thiazolinc 2 proves to be inert to organometallic attack. However, addition of organolithium and Grignard reagents to the C —N double bond of 2 can easily be achieved by previous activation with boron trifluoridc, providing /r[Pg.696]

The synthesis of alkoxy amines 2 by addition of organometallic reagents to the C-N double bond of oxime ethers 1 is plagued by the propensity for proton abstraction a. to the C-N double bond, the lability of the N-O bond and the poor electrophilicity of the oxime ethers. Therefore, frequently no products, undesired products or complex mixtures are obtained. The result depends on the substrate, organometallic reagent, solvent, temperature and additives1 6. 

Abstract The use of A-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation. 

Fernandez, E.J., Gimeno, M.C., Jones, P.G., Laguna, A. and Olmos, E. (1997) Strong Activation of the Double Bond in (PPh2)2C CH2. Novel Synthesis of Gold (111) Methanide Complexes by Michael Addition Reactions. Organometallics, 16 (6), 1130-1136. 

In contrast with the behaviour of typical vinylphosphonic acid derivatives, the carbon-carbon double bond in the 1,2-oxa-phospholene (167) is remarkably unreactive towards a broad spectrum of reagents including electrophiles, most epoxidizing and organometallic reagents, as well as to dipolar addition reactants. Exceptional reagents are, however, N-bromoacetamide (NBA), ozone, dimethyllithiumcuprate, and sodium-naphthalene. 

The double bond of butenolides undergoes stereoselective Michael addition of organometallic reagents, affording useful synthetic intermediates. Thus 1,4-addition of lithium dimethylcuprate to 231 gave 236 as a single isomer, which was employed (237) for the synthesis of the bromopentene derivative 237. 

Lithium-ammonia reduction of a,/ -unsaturated ketones (entry 6, Scheme 1.4) provides a very useful method for generating specific enolates.26 The desired starting materials are often readily available, and the position of the double bond in the enone determines the structure of the resulting enolate. This and other reductive methods for generating enolates from enones will be discussed more frilly in Chapter 5. Another very important method for specific enolate generation, the addition of organometallic reagents to enones, will be discussed in Chapter 8. 

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