Addition organometallic reagent

Reactivity and selectivity of organometallic reagents addition to C=N bond with participation and formation of heterocycles 98CRV1407. 

This is a reaction with high atom economy and without the use of organometallic reagents, additives, or redox systems. Such an acetoxypalladation-initiated carbon-heteroatom multiple bond insertion-protonolysis system may extend the scope of transition metal-catalysed reactions pertaining to the insertion of carbon-heteroatom multiple bonds into metal-carbon bonds, and provide a new methodology in organic synthesis. The generality of the present catalytic system is shown in Table 10.2.[3]... 

Aldehydes are "prochiral", thus addition of an organometallic reagent to an aldehydes may be stereoselective,... 

The ketones can be obtained by addition of organometallic reagents to acids and their derivatives. 

Dihydropyrazines are relatively stable, although they are easily oxidized. They are usually formed via the addition of organometallic reagents to the pyrazine ring. Similarly, 2,3-dihydropyrazines are usually easily oxidized to pyrazines and are formed during type A synthesis (see Section 2.14.3.2). 

Carbanions are very useful intermediates in the formation of carbon-carbon bonds. This is true both for unstabilized structures found in organometallic reagents and stabilized structures such as enolates. Carbanions can participate as nucleophiles both in addition and in substitution reactions. At this point, we will discuss aspects of the reactions of carbanions as nucleophiles in reactions that proceed by the 8 2 mechanism. Other synthetic aj lications of carbanions will be discussed more completely in Part B. 

There is another possible mechanism for addition of organometallic reagents to carbonyl compounds. This involves a discrete electron-transfer step. °... 

Table 8.2. Stereoselectivity in Addition of Organometallic Reagents to Some Chiral Aldelqrdes and Ketones"...

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. 

Similarly, the addition of organometallic reagents to pyridines leads to dienamine intermediates, which can be demonstrated (167-170). 

Reaction of Nitriles with Organometallic Reagents Grignard reagents add to a nitrile to give an intermediate imine anion that is hydrolyzed by addition of water to yield a ketone. 

Nitriles are similar in some respects to carboxylic acids and are prepared either by SN2 reaction of an alkyl halide with cyanide ion or by dehydration of an amide. Nitriles undergo nucleophilic addition to the polar C=N bond in the same way that carbonyl compounds do. The most important reactions of nitriles are their hydrolysis to carboxylic acids, reduction to primary amines, and reaction with organometallic reagents to yield ketones. 

In his original paper,2 Cram disclosed an alternative model that rationalizes the preferred stereochemical course of nucleophilic additions to chiral carbonyl compounds containing an a heteroatom that is capable of forming a complex with the organometallic reagent. This model, known as the Cram cyclic or Cram chelate model, has been extensively studied by Cram9 and by others,410... 

The reaction of 3-benzoxepin with methyllithium results in the addition of two equivalents of the organometallic reagent and cleavage of the heterocycle. After hydrolysis l-[2-(Z)-prop-l-enyl)phenyl]propan-2-ol can be isolated, but no experimental data is available.216 Occasionally, a small amount of the tran.v-isomcr is obtained (less than 10% of the product).12... 

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