Organocerium reagents, with

Table 1 The Reaction of Organocerium Reagents with Ketones...

Amides, especially of piperidine and morpholine, give good yields of ketones on reaction with organocerium reagents.203 It has been suggested that the morpholine oxygen may interact with the oxyphilic cerium to stabilize the addition intermediate. 

Barbier-type organocerium reagents reacted with Af,Af-bis[(A)-l-phenylethyl]ethanediimine 31 to form 1,2-aminoal-cohol 32 via hydrolysis of the initially formed iminoamine product by water released from CeCl3 hydrate (Scheme 10).17 Aminoalcohol 32 was produced as a sole product. 

Several reviews and research papers discussing the application and extension of this method have appeared.40 For example, Weber et al.41 reported an interesting result in which cerium acted as a counterion in the modified proline auxiliary (SAMEMP 40) for selective addition of organocerium reagents to hydrazones. The initial adduct was trapped with either methyl or benzyl chloro-formate to afford the stable /V-aminocarbonatc 41 (Scheme 2-24). From this example readers can see that this proline chiral auxiliary can be used not only for a-alkylation but also for nucleophilic addition, which is discussed in detail later. 

In the study of Weber et al.,41 a series of proline-derived hydrazones were prepared, and the reactions of the hydrazones with organocerium reagents were examined. It is clear from the table in Scheme 2 24 that the diastereoselectivity of the examined reactions depends on the nature of the side chain. (S )-l-amino-2-(2-methoxyethoxymethyl) pyrrolidine (40) gave the highest selectivity for various nucleophiles. 

A most remarkable reaction of Grignard reagents with a l-(oxazolidin-2-yl)naphthalene has been described, in which addition to the aromatic ring occurs, whereas organolithium, organocerium or organocopper reagents all attack the oxazolidine 2-position [20] ... 

Organocerium reagents are prepared in situ by the reaction of organolithium compounds with anhydrous cerium chloride or ceriiun iodide, as shown in equation (1). A variety of organolithium compounds can be employed, including alkyl-, allyl-, alkenyl- and alkynyl-lithiums, which are all converted to the corresponding cerium reagents. 

The addition reactions are usually carried out at -78 °C, except for reactions of the Grignard re-agent/cerium chloride system (Section 1.8.4), which are conducted at 0 °C. A substrate is added to the well-stirred organocerium reagent and the mixture is stirred until the reaction is complete. Work-up is carried out in the usual manner quenching with dilute HCl or dilute AcOH and extraction with a suitable organic solvent. When the substrates are acid sensitive, work-up using tetramethylenediamine is recommended. ... 

Organocerium reagents react with a,3-unsaturated carbonyl compounds to give 1,2-addition products in good to high yields (equation 2). 2 ... 

The reaction of cerium reagents with imines and nitriles which possess a-hydrogens has been studied by Wada et al ° Available data indicate that the reagents do not effectively d to these substrates, although the results are better than with alkyllithiums themselves. A modification of the procedure improves the yields of addition products. Thus, addition of the organocerium or organolithium reagent to an... 

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