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racemicinthesecases.Acatalyticenantioselectiveborohydridereductionofaromaticketonesusinganopticallyactivecobalt(II)complexcatalyst7wasre-ported(Eq.(73))[84].

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Thelanthanoidcomplexes,tris{4-(l-menthyloxy)-1-(p-tolyl)butane-1,3-dionato}-lanthanoid(III),[Ln(l-moba-Me)3]facilitateenantioselectiveborohydridereductionofketones(Eq.(74))[85].Thereactionisstoichiometriconthechirallanthanoidcomplex.How-ever,thehostcomplexesarereadilyrecoveredingoodyieldsforuseagain.

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Theuseofmontmorilloniteclayintheasymmetricreductionofketonesusing(-)-N-dodecyl-N-methylephedreniumborohydridewasinvestigated(Eq.(75))[86].Theratesofreductionsarequitefastbothinpolaraswellasinnon-polarsolvents.However,theasym-metricinductionsrealisedwereonlypoor.

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Thechirallymodi edCu2+

–montmorillonitehasbeenpreparedusing( )-2-amino-1-propanoland(S)-proline.Theketonepre-adsorbedonthisclaywasreducedbytheadditionofNaBH4inethanolwithlowasymmetricinductions(Eq.(76))[87].Theadvantageofthissystemisthereusabilityofthechiralmoiety.

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Thechiralreversemicellesformedfromchiralsurfac-tants8areusefulfortheasymmetricreductionofprochiralketoneswithNaBH4(Eq.(77))[88].Itwasnoticedthattheenantioselectivityofthereactionisaffectedbythestructuresofbothsurfactantandsub-strate.Also,theresultsdependonthecompositionofthemicroenvironment.Further,itwasreportedthatthepresenceofsomesugarsincreasestheenantiomericexcessoftheproducts.

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10.4.Reducti6eaminationofaldehydesandketones

ThereactionsofaldehydesorketoneswithNH3,primaryaminesorsecondaryaminesinthepresenceofreducingagentstoobtainprimary,secondaryorter-tiaryamines,respectivelyareamongthemostusefulandimportantprocessesforthesynthesisofdifferentamines.Thechoiceofthereducingagentisveryimpor-tantforthesuccessofthereactionsincethereducingagentmustreducetheimines(oriminiumsalts)inter-mediatesselectivelyoveraldehydesorketonesunderthereactionconditions(Eq.(78)).

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TheNaBH4suitswellforsuchapplications.Forexample,reductivealkylationofamineswerebereadilycarriedoutusingNaBH4inneatliquidcarboxylicacids(Eq.(79))[89].Also,reductiveaminationofaldehydesandketoneswerereportedusingsodiumtriacetoxy-borohydride[90].

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