Organocerium compounds

Organocerium compounds were also found to be the preferred organometallic reagent for addition to hydrazones in an enantioselective synthesis of amines  

Larock, Organomercury Compounds in Organic Synthesis, Springer-Verlag, Berlin, 1985. B. J. Wakefield, The Chemistry of Organolithium Compounds, Pergamon, Oxford, 1974 B. J. Wakefield, Organolithium Methods, Academic Press, Orlando, Florida, 1988. 

Predict the product of each of the following reactions. Be sure to specify all elements of stereochemistry. 

Reaction of the epoxide of 1-butene with methyllithium gives 3-pentanol in 90% yield. In contrast, methylmagnesium bromide under similar conditions gives the array of products shown below. Explain the difference in the reactivity of the two organometallic compounds toward this epoxide. 

Devise an efficient synthesis for the following organometallic compounds from the starting material specified. 

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Addition of organocerium compounds to menthone was reported in 2000 (Scheme 3).6 The use of organocerium compounds instead of organomagnesium reagents or organolithium compounds resulted in an enhancement of the yields of 9 in almost all cases examined. 

As emphasized above, the practical utility of organocerium compounds is to circumvent the problems which are faced with the corresponding Grignard and organolithium reagents because of their inability to react effectively with sterically demanding carbonyl compounds and carbon-heteroatom unsaturated bonds which have acidic a-protons. Some of the latest examples are shown below. 

Reaction of anhydrous cerium(iii) chloride with RLi reagents affords organocerium compounds The cerium chloride is prepared by heating CeCl3(H20)7 in vacuo up to 140 °C and is in fact a monohydrate [CeCl3(H20)], see W.J. Evans, J.D. Feldman, and J.W. Ziller, J. Am. Chem. Soc., 1996,118,4581. Reaction is carried out at -78 °C, as decomposition is rapid at 0 °C, especially if a /3-hydrogen is present in the R group. The exact nature of the cerium species is uncertain. 

A How are organocerium compounds prepared Why are they useful Why can CeCl3/NaBH4 be used in the presence of water, whilst CeCl3/LiAlH4 requires strictly anhydrous conditions ... 

AUcylhthium compounds smoothly reduce Ce(acac)4 to the cerium(III) derivative Li[Ce (acac)4]. On increasing the Li/Ce molar ratio, organocerium compounds of composition Li3[CeR3(acac)3] are formed. With Grignard reagents, products of the type Ce(acac)3 RMg (acac) are obtained . 

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