Organocerium reagents reactions

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. 

A similar but bulkier organocerium reagent 26 was applied to the total synthesis of bilosespenes A and B.1S Upon reaction of 26 and ketone 25, the target intermediate 27 was obtained in 76% yield as a single isomer (Scheme 9). 

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. 

Attempts to extend these reactions to the synthesis of simple hydroxylamines were plagued by deprotonation and redox side-reactions, but recently yields have been much improved by conversion of the Grignard reagent into an organocerium reagent in situ [12] for example, yV-butyl-A-propylhydroxylamine was prepared in 90% yield. Another successful variant utilized A-nitrosodiphenylamine to generate a nitroso compound in situ. The hydroxylamine salt produced was oxidized in situ to give a nitroxide [13] ... 

This chapter surveys the addition reactions of organocerium reagents to the C—rr-bond. Emphasis is placed on the utility of cerium chloride methodology, and many examples of its practical applications... 

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. ... 

The stereochemistry in the reactions mentioned above is consistent with a chelation-controlled addition of the organocerium reagents. On the other hand, nonchelation-controlled addition of alkylcerium reagents to carbonyl components has also been observed, as shown in Scheme... 

Recently, Mudryk and Cohen have found that reactions of lactones with organocerium reagents provide lactols in go yields, as exemplified in Scheme 10. This reactiim leads to an efficient (xie-pot synthesis of spiroketais, as illustrated in Scheme 11. ... 

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