Reduction cerium chloride

Nicolaou and coworkers have reported an expeditious IBX (2-iodo3gr-benzoic acid, l-hydro q -l, 2-benziodoxol-3(l//)-one 1-oxide) mediated synthesis of Z-vancosamine " starting from vinyl iodide and protected aldehyde via an intramolecular Kishi-Nozaki coupling reaction. The coupling product, as a mixture of alcohols, was immediately oxidized with DMP (Dess-Martin periodinane). The oxidation was followed by a sodium borohydride/cerium chloride reduction to produce a protected alcohol intermediate. In the next step, the required alcohol was reacted... 

A particularly useful reaction has been the selective 1,2-reduction of a, P-unsaturated carbonyl compounds to aHyUc alcohols, accompHshed by NaBH ia the presence of lanthanide haUdes, especially cerium chloride. Initially appHed to ketones (33), it has been broadened to aldehydes (34) and acid chlorides (35). NaBH by itself gives mixtures of the saturated and unsaturated alcohols. 

Correct reagent selection allowed reduction of steroidal enone (74) to either diastereoisomeric allylic alcohol, uncontaminated by its isomer. Sodium borohydride/cerium chloride in methanol-THF gave the equatorial alcohol (73), while L-selectride produced the axial isomer (75) via equatorial attack (Scheme 12). Unexpected axial attack on diketone (76) to give equatorial alcohol (77 equation 19) led to the proposition that for hydride additions to decalones two 1,3-diaxial interactions override one peri interaction which in turn takes precedence over a single 1,3-diaxial interaction. ... 

In spite of substantial evidence, the tendency for sodium borohydride to reduce enones in a conjugate sense is often ignored, but the need for reduction to the corresponding allylic alcohols has led to the development of several new specific reagent combinations. The most widely accepted of these involves sodium borohydride in the presence of cerium chloride, which has been optimized to give excellent... 

Representative examples of the reactions of various carbonyl compounds with Grignard reagents under these conditions are listed in Table 5. It is emphasized that enolization, aldol reaction, ester condensation, reduction and 1,4-addition are remarkably suppressed by the use of cerium chloride. Various tertiary alcohols, which are difficult to prepare by the conventional Grignard reaction, can be synthesized by this method. 

Derivation (1) Calcium reduction of vanadium pentoxide yields 99.8+% pure ductile vanadium (2) aluminum, cerium, etc. reduction produces a less pure product (3) solvent extraction of petroleum ash or ferrophosphorus slag from phosphorus production (4) electrolytic refining using a molten salt electrolyte containing vanadium chloride. 

Warren has used a variation of his phosphine oxide-based olefination method to synthesise single isomers (E or Z) of unsaturated carboxylic acids.23 a-Diphenylphosphinoyl ketones (32) are reduced by sodium borohydride to give diastereomeric mixtures of the corresponding alcohols (33) and (34). These alcohols can be converted to the lactones (35) and (36) which can be separated and individually converted stereospecifically into (Z)-(37) and (E)-(38) alkenes by base treatment (Scheme 6). In many cases it is possible to reduce p-ketophosphine oxides (39) and enones (41) stereoselectively to the ery/Aro-alcohols (40) and (42), respectively, using sodium borohydride in the presence of cerium chloride (Scheme 7).24 An earlier report that reduction in the presence of cerium salts did not cause reversal of stereochemistry compared to reduction with borohydride alone appears to be true only of the compounds studied in that report. The carbanions of 3-hydroxypropylphosphine oxides (43) have been reported to undergo O- to C-acyl transfer to give the p-ketoalkylphosphine oxides... 

One of the limitations of the Warren s adaptation of Homer-Wittig olefina-tion, the failure of the (Z)-selective route when the alkene has a branched chain substituent, has now been overcome. Reduction of the p-ketophosphonates carrying a-branches, e.g. (112) and (113), with sodium borohydride and cerium chloride gives excellent a / -stereoselectivity and hence (Z)-alkene on base-induced elimination. Enantioselective synthesis of both jy -(115) and anti- ll) P-hydroxy-phosphine oxides has been achieved with up to 90% e.e. through two separate approaches. The jyn-isomer was obtained by reduction of the corresponding ketone (114), while the anti-isomer is the product of the reaction of the oxazolidine substituted aldehyde (116) with lithiated diphenylmethyl-phosphine oxide (Scheme 10). A new, highly stereoselective approach to trisubstituted alkenes has been reported. Cerium(III) chloride-promoted... 

Reduction of enones. Sodium borohydride in combination with catalytic amounts of cerium chloride reduces a,/8-unsaturated ketones selectively to allylic alcohols. Reactions proceed within 5 minutes even at 20°. ... 

Trost coined the term chemoselective to describe the process where one of two similar functional groups is made to react, while the other is not affected or affected to a lesser extent [1]. This discrimination usually results from nuanced changes to a reagent s behavior, e.g., by addition of a salt. A typical example is the modification of sodium borohydride reduction by addition of cerium chloride in the Luche process, whereby the double bond of an ot-enone is not saturated during the reaction [85]. Similarly, a new approach to chemoselective reaction of n-pentenyl donors was soon to emerge. 

It was Carl Gustaf Mosander (Figure 17.8), from 1836 Berzelius successor as professor of chemistry, who started the great work of separating the almost inseparable. As Berzehus student from 1820 he soon came into his service. He prepared cerium sulfide and let it react with chlorine. Anhydrous cerium chloride CeClj, was formed, from which he prepared metalHc cerium by reduction with potassium metal. This was in about 1825. With all his work with different cerium compounds he began to... 

Several reagents have been developed which lead to exclusive 1,2- or 1,4-reduction. Use of NaBH4 in combination with cerium chloride results in clean 1,2-reduction. Diisobutylaluminum hydride " and the dialkylborane 9-BBN also... 

Metallic cerium is prepared by metahothermic reduction techniques, such as reducing cerous fluoride with calcium, or using electrolysis of molten cerous chloride or others processes. The metahothermic technique produces high-purity cerium. 

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