Organolithium reagents, addition aldehydes

The Addition of Grignard Reagents and Organolithium Reagents to Aldehydes and Ketones... 

An ability to form carbon-carbon bonds is fundamental to organic synthesis. The addition of Grignard and organolithium reagents to aldehydes and ketones is one of the most frequently used reactions in synthetic organic chemistry. Not only does it permit the extension of carbon chains, but because the product is an alcohol, a wide variety of subsequent functional group transformations is possible. 

Scheme 7.4 illustrates some of the important synthetic reactions in which organolithium reagents act as nucleophiles. The range of reactions includes S/v2-(ype alkylation (Entries 1 to 3), epoxide ring opening (Entry 4), and formation of alcohols by additions to aldehydes and ketones (Entries 5 to 10). Note that in Entry 2, alkylation takes place mainly at the 7-carbon of the allylic system. The ratio favoring 7-alkylation... 

By modification of method A, Jones has transformed 2,4-bis-OBoc-benzy-aldehyde 5 into the 3-carbomethoxy dihydrocoumarin 43 in 68% yield (Fig. 4.23).lla The reaction proceeds by the addition of phenyl Grignard followed by addition of a preformed mixture of methyl malonate and sodium hydride and warming to room temperature. This particular example obviates the need for prior initiation by an organolithium reagent. 

Scheme 2.38 Functionalized allenes formed by 1,4-addition of organolithium reagents to enynes and electrophilic trapping with aldehydes (111, 112) ketones (113,114), ethylene oxide (115) and carbon dioxide (116).

The asymmetric addition of organomagnesium and organolithium reagents to a,P-unsaturated carbonyl compounds and especially imines can be achieved in situations where rigid chelation controls the geometry of the transition state. Stereospecific alkyl addition occurs in the case of a chiral leucine-derived imine to provide overall asymmetric alkyl addition to an a,P-unsaturated aldehyde (Scheme 107).380 381... 

Several asymmetric 1,2-additions of various organolithium reagents (methyllithium, n-butyllithium, phenyllithium, lithioacetonitrile, lithium n-propylacetylide, and lithium (g) phenylacetylide) to aldehydes result in decent to excellent ee% (65-98%) when performed in the presence of a chiral lithium amido sulfide [e.g. (14)], 75 The chiral lithium amido sulfides invariably have exhibited higher levels of enantioselectivity compared to the structurally similar chiral lithium amido ethers and the chiral lithium amide without a chelating group. 

Alcohols can also be obtained from epoxides, aldehydes, ketones, esters, and acid chloride as a consequence of C-C bond formation. These reactions involve the addition of carbanion equivalents through the use of Grignard or organolithium reagents. 

Organolithium reagents reacts just like Grignard reagents. For example, reaction with aldehydes and ketones proceeds by nucleophilic addition to yield secondary and tertiary alcohols respectively. 

The mechanism of 1,2-nucleophilic addition is the same as already described. It is found that Grignard reagents and organolithium reagents will react with a,p-unsaturated aldehydes and ketones in this way and do not attack the p-position ... 

Other common, and commercially available, organolithium reagents include n-butyllithium and phenyllithium, and they react with both aldehydes and ketones. Note that addition to an aldehyde gives a secondary alcohol while addition to a ketone gives a tertiary alcohol. 

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