Carbonyl compounds organometallics

Jiang S, Agoston GE, Chen T, Cabal M-P, Turns E (1995) BF3 Et20-promoted allylation reactions of allyl(cyclopentadienyl)iron(II) dicarbonyl complexes with carbonyl compounds. Organometallics 14 4697 -709... 

Lin B, Gao M, Dang L, Zhao H, Marder TB, Lin Z. DFT stndies on the mechanisms of the platinnm-catalyzed diboration of acyclic a,P-unsaturated carbonyl compounds. Organometallics. 2012 31 3410-3425. 

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

The distinguishing feature of this mechanism is the second step, in which an electron is transferred fixim the organometallic reagent to the carbonyl compound to give the radical... 

The stereoselectivity of organometallic additions with carbonyl compounds fits into the general pattern for nucleophilic attack discussed in Chapter 3. With 4-r-butylcyclohex-anone, there is a preference for equatorial approach but the selectivity is low. Enhanced steric factors promote stereoselective addition. 

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

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 addition of an achiral organometallic reagent (R M) to a chiral carbonyl compound 1 (see Section 1.3.1.1.) leads to a mixture of diastercomers 2 (syn/anti) which can be either racemic, or enantiomerically enriched or pure, depending on whether the substrates are race-mates or pure enantiomers. This section incorporates only those reactions starting from optically pure a-amino aldehydes, however, optical purity of the starting material has not been demonstrated in all cases. 

In most cases of diastereoselective nucleophilic addition reactions where achiral organometallic reagents are added to chiral carbonyl compounds, the chirulity inducing asymmetric center is in close vicinity to the newly created center and cannot be removed without the loss of chirality of either the inducing center or the newly formed center. This type of reaction is very useful in propagating chirality in a molecule from one center to an adjacent one, or in immolative processes. 

As well as the addition of achiral organometallic reagents to chiral aldehydes (see also Sections 1.3.2. and 1.3.3.), the addition of chiral organometallic reagents to carbonyl compounds is a well-known and intensively studied process which may lead to enantiomerically and/or diastereomerically enriched products. Chiral organometallic reagents can be classified into three groups ... 

The first reports on enantioselective addition reactions of achiral organometallic reagents, modified by aprotic chiral additives, described the addition of Grignard reagents to prostereogenic carbonyl compounds in the presence of ( + )-(/ ,/J)-2,3-dimethoxybutane (l)4 5, (-)-tetrahydro-2-methylfuran (2)6, (-)-l-[(tetrahydro-2-furanyl)methyl]pyrrolidine (3)7 or (-)-sparteine (4)8. The enantioselectivity, however, was poor (0-22% ee). 

Formation of C-C Bonds by Addition of Allyl-Type Organometallic Compounds to Carbonyl Compounds... 

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

Addition of vinylic organometallic compounds to unsaturated carbonyl compounds addition of organometallic compounds to acetylenic carbonyl compounds... 

Grignard reagents are quite restricted in the types of functional groups that can be present in either the organometallic or the carbonyl compound. Alkene, ether, and acetal functionality usually causes no difficulty but unprotected OH, NH, SH, or carbonyl groups cannot be present and CN and NOz groups cause problems in many cases. 

The stereochemistry of addition of organometallic reagents to chiral carbonyl compounds parallels the behavior of the hydride reducing agents, as discussed in Section 5.3.2. Organometallic compounds were included in the early studies that established the preference for addition according to Cram s rule.118... 

Organopalladium intermediates are also involved in the synthesis of ketones and other carbonyl compounds. These reactions involve acylpalladium intermediates, which can be made from acyl halides or by reaction of an organopalladium species with carbon monoxide. A second organic group, usually arising from any organometallic reagent, can then form a ketone. Alternatively, the acylpalladium intermediate may react with nucleophilic solvents such as alcohols to form esters. 

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