Cerium chloride enones

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... 

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... 

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. 

Analogically to the coupling of alkynes with alkenes (enones) there is also coupling of allenes with enones to give the dienones 190 (Scheme 82). This process is catalyzed by a number of ruthenium complexes such as 78 or 53 in the presence of a catalytic amount of cerium chloride. The former catalyst is suitable... 

Dienes such as 90 can be accessed by a multi-component reaction under ruthenium catalysis involving an allene 88 and an enone (methyl vinyl ketone in this case), with cerium(m) chloride as an additive in DMF (Scheme 26).95,96 With an allene concentration of 0.25 M, yields are moderate to good. Different ruthenium catalysts and additives were tested in order to optimize this reaction. CpRu(COD)Cl 89 and CpRu(MeCN)3PF6 appeared to be more versatile ones. The mono-, di-, tri-, and tetrasubstituted allenes have been investigated with methyl vinyl... 

Both InBr3 and InCl3 mediate the conjugate addition of pyrroles and indoles to enones <2001S2165, 2002JOC3700>, without problems of acid-catalyzed oligomerization, e.g., Scheme 44. Cerium(III) chloride heptahydrate and sodium... 

Reduction of the enone 147 with sodium borohydride-cerium(Ill) chloride in methanol gave a 2 1 mixture of the unsaturated alcohols. 

Cerium(III) chloride polarizes su lectivities in Grignard reactions. / enones and nitroethylarenes, respc... 

Reaction with Carboxylic Acid Derivatives. Reaction of (1) with carboxylic acid derivatives provides silyl ketones (3) (eq 4). The reaction 3ueld is very dependent upon the presence of a-hydrogens in the substrate lower yields are obtained when deprotonation can occur at this center. The reaction occurs with esters, lactones, acid chlorides, and the parent carboxylic acids. The resultant /3-silyl ketones can be desilylated by simple hydrolysis, or used as a substrate in a Peterson alkenation approach to enones. The use of a cerium reagent with the acid chloride has been advocated for the preparation of allylsilanes. ... 

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