Borohydride cerium, reduction with

In the special case of a-alkyl-a -nitro-substituted imines, reduction with sodium borohydride/ cerium(III) chloride and elimination of the chiral auxiliary generated the nitroalkene without racemization22. 

As discussed above, the absolute stereochemistry of halenaquinone (+)-l and halenaquinol (+)-2 has been theoretically determined by the calculation of the CD spectra of naphthalene-diene derivatives by means of the tt-electron SCF-CI-DV MO method. 18 To apply the same method to these xestoquinone compounds, xesto-quinol dimethyl ether (+)-74 was converted to naphthalene-diene derivative 75 by reduction with sodium borohydride in the presence of cerium(IIl) chloride23 and methanol, followed by treatment with pyridinium p-toluenesulfonate and methanol (Scheme 16).20 The product obtained was a mixture of two stereoisomers of the methoxyl group at the 4-position, from which a single isomer 75 was isolated as... 

Sodium borohydride and potassium borohydride react regioselectively with the formyl group of alkyl 2-formylcyclopropanecarboxylates lithium aluminum hydride is unseleetive. Stereospecific reduction of the formyl group was observed when formyl-cyclo-propanes were subjected to yeast alcohol dehydrogenase. ei Furthermore, regiospecific reduction of the aldehyde function in a 2-cyclopropylprop-2-enal derivative was performed using a mixture of sodium borohydride and cerium(III) chloride. 

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

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... 

The Luche reduction involves a selective 1,2-reduction of a,p-unsaturated aldehydes and ketones using sodium borohydride in combination with cerium(III) chloride, resulting in the formation of allylic alcohols.1... 

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°. ... 

By far the widest application in organic synthesis for the cerium(III) species has involved its striking effects in selective reductions with sodium borohydride (section 5). 

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... 

Under appropriate experimental conditions, hydrogen telluride, phenyl tellurol, and sodium hydrogen telluride perform the selective reduction of double bonds of a,/3-unsaturated carbonyl systems.89 90 This reaction with a,j3-unsaturated ketones complements the cerium trichloride/sodium borohydride method, which reduces the carbonyl group, keeping the carbon-carbon double bond intact92 (Scheme 18). 

The subsequent transformation of these cycloadducts further illustrates the versatility of this approach in the construction of guaianolide sesquiterpenes (Scheme 1)7 The moiety incorporated in the adduct allows for the introduction of diverse functionalities at C-S and C-2. For example, reduction of the cycloadduct (11) with sodium borohydride produces a good yield of the iron complex (16). Oxidation of this complex with cerium ammonium nitrate gives methyl ester (17). In addition, (11) reacts with nucleophiles such as lithium dimethylmalonate and methanol to give the alkylated complex (18) and the meth-oxylated complex (19), respectively. Oxidative demetallation of (11) with bromine leads to selective replacement of the moiety at C-2 by bromide. ... 

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... 

This method was also applied to the reduction of natural products, using cerium(lll) chloride with sodium borohydride to minimize the formation of saturated alcohols and give good yields of allylic alcohols with good stereoselectivity (Luche et al., 1978). 

The selective reduction of the carbonyl function of a [4.4.4.]-propellatrienone to an allylic alcohol has been carried out with cerium(III) chloride-doped sodium borohydride (Paquette et al., 1984) en route to a unique tetraene derivative. 

Mono-addition of 4-benzyloxybutylmagnesium bromide to the acetal-protected L-tartaric acid bis(dimethylamide) 227 launched the synthesis of (4-)-lentiginosine (127) by Prasad and Pawar (Scheme 30). Reduction of the ketone (+)-228 formed in this way with sodium borohydride mediated by cerium trichloride gave the (R)-alcohol (—)-229 as an inseparable mixture of diastereomers (91 9). After mesylation and Sn2 reaction with... 

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