Additions of organometallic

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). 

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"...

Analyze the factors which would determine stereoselectivity in the addition of organometallic compoimds to the following carbonyl compounds. Predict the major product. 

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). 

The addition of organometallic reagents to a-amino ketones e.g., 1 normally obeys Cram s rule the dominant diastereomer is the. syrc-compound81. 

A different approach to chiral oc-hydroxy acids 4 is the nucleophilic addition of organometallic reagents to chiral oc-oxo 4,5-dihydrooxazoles 2, which can be synthesized by oxidation of the corresponding 2-alkyl-4,5-dihydrooxazoles l17,19. 

As with oxathianes 3 (R1 = CH, R2 = H), which bear a close structural resemblance to 17, the addition of organometallic reagents is highly diastereoselective with a predominant chelation-controlled attack of the nucleophile from the Rc-sidc35 -40. In the case of vinylmagnesium bromide a considerable enhancement of the diastereo selectivity could be attained by adding... 

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 ... 

For diastereoselective addition of organometallic agents to imines attached to arene tricar-bonylchromium or ferrocenyl moieties, see refs 26 28 and Section 1.4.1.1.2.2. 

Arylalkylamines 6 by Addition of Organometallic Reagents to 1,3-Oxazolidines 4 and Oxidative Cleavage and Hydrolysis General Procedure22 ... 

Additions of organometallic compounds to 2-azelidinones such as 1 or 4 bearing a leaving group in the 4-position preferentially or exclusively afford tram-3,4-substituted /(-lactams 3 or 6. Therefore, the participation of an A -acylinline intermediate such as 2 or 5 which is attacked from the less hindered side is probable14-16. This has been exploited for the synthesis of carbapenem antibiotics, e.g., thienamycin (7)16. 

The enantioselective addition of organometallic reagents to, V-(trimethylsilyl)benzaldehyde imine (1) in the presence of enantiomerically pure modifiers has been investigated. The best result is obtained with butyllithium (the corresponding Grignard reagent affords both lower yield and selectivity, 1 fails to react with diethylzinc) and two equivalents of the enantiomerically pure diol 2 in diethyl ether. It should be noted that the choice of the solvent is crucial for the stereoselectivity of the reaction1 2 3 5 7 8 9. 

Addition of organometallics to hydrazones provides hydrazines1, which can be converted to the corresponding amines by hydrogenolysis. Hydrazones can therefore be regarded as masked imine derivatives of ammonia. This methodology has been utilized successfully for numerous stereoselective syntheses of amines and amine derivatives2-23. 

Table 4. Addition of Organometallics to Chiral /V,jV-Dimethyl Hydrazone Aminals Sb6,7 HsCe,...

In order to synthesize 1,3-diphenyl-l, 3-diamines 3 containing a C2 axis of symmetry, which can be employed as auxiliaries and controller groups in asymmetric syntheses, the diastereoselective addition of organometallic reagents to racemic pyrazolines 2, prepared from cinnamaldehyde (l)23, was investigated. 

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. 

Table 6. Addition of Organometallic Reagents to Racemic Nitrones S8-9...

Table 8. 1,2-Asymmetric Induction in the Addition of Organometallics to N-Alkylimines 4, Cram Selectivity 6...

Addition of Organometallic Compounds to a,/MJnsaturated Carbonyl Compounds... 

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