Organomagnesium compounds, reaction bonding

Under the conditions used for the reductive cleavage of the O—N bond in isoxazoles, a similar reaction readily occurs with isoxa-zolines, e.g. on treatment with organomagnesium compounds and on catalytic hydrogenation.- Hydrogenolysis of the O—N bond (180 181 182 183) was used to elucidate the structure of isoxa-zolones from -ketoesters. -... 

Uncatalyzed addition reactions of Grignard reagents with nonconjugated alkenes and aUcynes are of limited use in synthesis. However, carbon-carbon double bonds substituted by a leaving group, such as an acetate, are susceptible to be displaced by organomagnesium compounds presumably by an addition-elimination pathway. A few examples have been reported (equation 64). 

The carbomagnesiation reaction proceeds with a range of organomagnesium compounds (Scheme 30) °. Not only aryl, alkenyl and aUcynyl groups, but also alkyl groups were found to add across a triple bond. The enhanced reactivity of cyano-substituted alkynes is worthwhile, and this may be due to accelerated alkyl transfer from 53 with activation of the cyano group by MgX2 (Scheme 29). 

C-Alkylations have been performed with both support-bound carbon nucleophiles and support-bound carbon electrophiles. Benzyl, allyl, and aryl halides or triflates have generally been used as the carbon electrophiles. Suitable carbon nucleophiles are boranes, organozinc and organomagnesium compounds. C-Alkylations have also been accomplished by the addition of radicals to alkenes. Polystyrene can also be alkylated under harsh conditions, e.g. by Friedel-Crafts alkylation [11-16] in the presence of strong acids. This type of reaction is incompatible with most linkers and is generally only suitable for the preparation of functionalized supports. Few examples have been reported of the preparation of alkanes by C-C bond formation on solid phase, and general methodologies for such preparations are still scarce. 

Reaction between quinuclidin-3-one (2) and organolithium or organomagnesium compounds is a general method for preparing tertiary alcohols.47,162,164-168 By dehydration of these alcohols substances with a semicyclic double bond (127) are formed together with A 2-dehydroquinuclidine derivatives (126).165-168 Reduction of unsaturated compounds gave various 3-substituted quinuclidines (128). 

Transition metal-catalyzed cross-coupling reaction has become the most important method for the formation of aryl-aryl bonds. The reaction of aryl halides and sulfonates with organomagnesium compounds is usually referred... 

Thirty years ago it was reported that reactions of Grignard reagents with 1-alkenes, catalysed by titanium tetrachloride, lead to organomagnesium compounds, formally derived by addition of HMgX to the carbon-carbon double bond [50,51], e.g. 

A number of reactions of organomagnesium compounds, giving rise to new organomagnesium compounds, are covered in other chapters. They include addition to carbon-carbon multiple bonds (see Chapter 4), addition to isonitriles (see Section 5.4), addition to carbon monoxide (see Section 6.5), thiophilic addition to carbon-sulfur double bonds (see Chapter 7) and addition to carbenes (see Section 9.1). 

The addition of organomagnesium compounds to the carbonyl group of aldehydes and ketones has a long history, and remains one of the most important reactions for carbon-carbon bond formation. While the overall reaction is simple, it is susceptible to a number of side-reactions, and its... 

Reactions of organomagnesium compounds with nitroso or nitro compounds are often complicated, and not useful in synthesis, or only represented by isolated examples. One exception to this generalization involves conjugate addition to a,[3-unsaturated and aromatic nitro compounds (see Section 4.2), and two others lead to the formation of carbon-nitrogen bonds. 

A number of reactions of organomagnesium compounds with compounds containing nitrogen-nitrogen multiple bonds give products containing new carbon-nitrogen bonds [A, E], but few of them are useful in synthesis. The main exceptions are reactions with azides, and some reactions of diazonium salts. 

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