Organometallic compounds, addition aldehydes

Various chiral diaminoalcohols (91, 92, 93, 94) were synthesized starting from commercially acailable (S)-proline. The enantioselective addition of organometallic compounds to aldehydes in the presence of the aminoalcohols was investigated. 

The Addition of Organometallic Compounds to Aldehydes and Ketones O-Hydro-C-alkyl-addition... 

Concerning reversal of diastereoselectivity in the BF promoted addition of crotyl-organometallic compounds to aldehydes, Y. Yamamoto and K. Maruhama,... 

The carbonyl group of acid derivatives reacts with the nucleophilic carbanion available from organo-metallic reagents. However, the reactions of the individual classes of compounds are not as straightforward as the addition reactions of organometallic compounds with aldehydes and ketones. Addition of a carbanion to the acyl carbon atom generates a tetrahedral intermediate that can decompose to give a ketone that will react further with another equivalent of the carbanion. 

As with the reduction of aldehydes and ketones (16-23), the addition of organometallic compounds to these substrates can be carried out enantioselectively and diastereoselectively. Chiral secondary alcohols have been obtained with high ee values by addition to aromatic aldehydes of Grignard and organolithium compounds in the presence of optically active amino alcohols as ligands. ... 

One of the important new directions in the study of addition reactions of organozinc compounds to aldehydes is the use of ionic liquids. Usually, application of these compounds in reactions with common organometallic reagents has a serious problem ionic solvents are usually reactive toward them, particularly Grignard and organolithium derivatives. It has been recently reported that carbonyl compounds react with allylzinc bromide formed in situ from allyl bromide and zinc in the ionic liquid 3-butyl-l-methylimidazolium tetrafluoroborate, [bmim][BF4].285 Another important finding is that the more reactive ZnEt2 alkylates aldehydes in a number of ionic liquids at room temperature.286 The best yields (up to 96%) were obtained in A-butylpyridinium tetrafluoroborate, [bpy][BF4] (Scheme 107). 

Organometallic compounds or carbanions undergo a number of reactions in which the carbanion or carbanion-like moiety of the organometallic compound acts as a nucleophilic displacing agent. Examples are the formation of hydrocarbons from alkyl halides, alkyl halides from halogens, and ketones from acid chlorides or esters. The latter two reactions are closely related to the base-catalyzed condensations and are perhaps additions as well as displacement reactions. Related addition reactions are the carbonation of organometallic compounds and the addition to ketones or aldehydes. 

SCHEME 22. Stereochemical outcome of the addition of polar organometallic compounds R"M to a-alkoxy aldehydes and ketones (G = protecting group)... 

For the addition of an organometallic compound to an imine to give a primary amine, R in RCH=NR would have to be H, and such compounds are seldom stable (6-13). However, the conversion has been done, for R = aryl, by the use of the masked reagents (ArCH=N)2S02 [prepared from an aldehyde RCHO and sulfamide (NH2)2S02]. Addition of R MgX or R"Li to these compounds gives ArCHR"NH2 after hydrolysis.481... 

There are many addition reactions of a,(3-unsaturated aldehydes, ketones, and related compounds that are the same as the carbonyl addition reactions described previously. Others are quite different and result in addition to the alkene double bond. Organometallic compounds are examples of nucleophilic reagents that can add to either the alkene or the carbonyl bonds of conjugated ketones (see Section 14-12D). Hydrogen cyanide behaves likewise and adds to the carbon-carbon double bond of 3-butene-2-one, but to the carbonyl group of 2-butenal ... 

In Section 6.5 you learned that the acylations of hydride donors or of organometallic compounds, which give aldehydes or ketones, often are followed by an unavoidable second reaction the addition of the hydride or organometallic compound to the aldehyde or the ketone. In this chapter, we will study the intentional execution of such addition reactions. 

A /3-hydroxysilane, like the one shown in Figure 4.38 (top, left), can be prepared stereo-selectively (e.g., via the Cram-selective reduction of an a-silylated ketone according to the reactions in Figure 8.9 or via the Cram-selective addition of organometallic compounds to a-silylated aldehydes similar to what is shown in Table 8.3). These compounds undergo a stereoselective anft -elimination in the presence of add and a stereoselective syn-elimination in the presence of a base (Figure 4.38). Both reactions are referred to as Peterson olefination. The stereochemical flexibility of the Peterson elimination is unmatched by any other HetVHet2 elimination discussed in this section. 

The reactions of organometallic reagents such as organolithium [696], -zinc [697-700], -magnesium [701], and -aluminum species [702] are facilitated by the presence of TiCU [9] as exemplified in Eq. (308) [703]. Even addition of a titanium compound to aldehydes was promoted in the presence of an extra amount of a titanium salt (Eq. 309) [704,705]. Titanium Lewis acids increase the reactivity of the a-position of a ketone (Eq. 310) [706] and the /3-position of an a,/3-unsaturated carbonyl compound towards nucleophiles (Eq. 311) [608,707-709]. The positive role of TiCU in the photo-hydroxymethylation of ketones and aldimines is ascribed to activation of methanol by the titanium salt (Eq. 312) [710]. 

---