Organomagnesiums addition

The mechanism is illustrated with the addition of a malonate anion across the double bond of ethyl cinnamate. The reaction is reversible in protic solvents and the thermodynamically most stable product usually predominates. When organometallic reagents are used as Michael donors (e.g., copper-catalyzed organomagnesium additions) SET-type mechanisms may be operational. 

Organomagnesium reagent capable of reacting with active H compounds or in additions to C X... 

An interesting example of the organomagnesium synthesis is to be found in the use of 1,4-addition of the Grignard reagent to 4-alkyl-ideneisoxazol-5-ones (91) to prepare saturated isoxazol-5-ones (92). 

Addition of organomagnesium compounds to polarized multiple bonds O OMgX OH... 

The organozinc compound 2 is less reactive than an organomagnesium compound the addition to an ester carbonyl group is much slower than the addition to an aldehyde or ketone. Nevertheless the addition of 2 to the carbonyl group of unreacted a-halo ester 1 is the most frequently observed side-reaction ... 

The much simpler steroid, 253, was fortuitously found to fulfill this role when injected into animals. Its lack of oral activity was overcome by incorporation of the 7a-thioacetate group. Reaction of the ethisterone intermediate, 77b, with a large excess of an organomagnesium halide leads to the corresponding acetylide salt carbonation with CO2 affords the carboxyllic acid, 251. This is then hydrogenated and the hydroxy acid cy-clized to the spirolactone. Oppenauer oxidation followed by treatment with chloranil affords the 4,6-dehydro-3-ketone (254). Conjugate addition of thiolacetic acid completes the synthesis of spironolactone (255), an orally active aldosterone antagonist. ... 

The reduction of carbonyl compounds by reaction with hydride reagents (H -) and the Grignard addition by reaction with organomagnesium halides (R - +MgBr) are examples of nucleophilic carbonyl addition reactions. What analogous product do you think might result from reaction of cyanide ion with a ketone ... 

Most successful approaches involving addition reactions in the presence of chiral additives utilize organolithium, organomagnesium and the recently introduced organotitanium reagents, which are known to coordinate with amines, ethers, metal amides and alkoxides. 

As demonstrated, the organozinc reagent provides exclusively the Cram product, while the organomagnesium reagent shows poor diastereofacial selectivity in the addition to 1 and even reverses the selectivity in the addition to 4. 

Arylboronic acids have traditionally been prepared via the addition of an organomagnesium or organolithium intermediate to a trialkyl borate. Subsequent acidic hydrolysis produces the free arylboronic acid. This limits the type of arylboronic acids one can access via this method, as many functional groups are not compatible with the conditions necessary to generate the required organometallic species, or these species may not be stable intermediates. 

While the synthesis of fnnctionalised secondary alcohols and amines can be achieved withont catalyst by the addition of organolithium and organomagnesium reagents to C=N and C=0 gronps, these methods lack a significant functional group tolerance. In order to overcome this limitation and access to more functionalised compounds, the catalytic arylation of aldehydes and imines has been extensively studied [2]. 

Addition of an excess of organolithium or organomagnesium reagents to germanium halides results in the deplacement of the halide ions and the formation of tetra-alkyl and -arylgermanium compounds. Representative examples of these reactions are shown in equations 4 and 5, respectively. 

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