Calcium borohydride

Compound 7 is reduced to 2-benzamidocinnamyl alcohol by calcium borohydride in hydroxylic solvents at low temperatures. This reduction had been accomplished previously using lithium aluminum hydride in tetrahydrofuran. 

Complex aluminum and boron hydrides can contain other cations. The following compounds are prepared by metathetical reactions of lithium aluminum hydride or sodium borohydride with the appropriate salts of other metals sodium aluminum hydride [55], magnesium aluminum hydride [59], lithium borohydride [90], potassium borohydride [9i], calcium borohydride [92] and tetrabutylammonium borohydride [95]. 

The reduction of ketones containing nitro groups to nitro alcohols is best carried out by borohydrides. 5-Nitro-2-pentanone was converted to 5-nitro-2-pentanol in 86.6% yield by reduction with sodium borohydride at 20-25°. Other nitro ketones gave 48.5-98.7% yields, usually higher than were obtained by Meerwein-Ponruiorf reduction [907]. 2-Acetamido-3-(p-nitrophenyl)-l-hydroxypropan-3-one was reduced with calcium borohydride at — 30° to 70% of threo- and 10% of er7tAro-2-acetamido-3-(p-nitrophenyl)propane-l,3-diol while sodium borohydride afforded a mixture of the above isomers in 25% and 47% yields, respectively [902]. 

More reliable therefore is reduction with lithium aluminum hydride, lithium borohydride or calcium borohydride, which do not hydrogenolyze hydroxy groups [92]. 

In aqueous solutions, calcium chloride undergoes double decomposition reactions with a number of soluble salts of other metals to form precipitates of insoluble calcium salts. For example, mixing solutions of calcium chloride with sodium carbonate, sodium tungstate and sodium molybdate solutions precipitates the carbonates, tungstates, and molybdates of calcium, respectively. Similar precipitation reactions occur with carboxylic acids or their soluble salt solutions. CaCb forms calcium sulfide when H2S is passed through its solution. Reaction with sodium borohydride produces calcium borohydride, Ca(BH4)2. It forms several complexes with ammonia. The products may have compositions CaCl2 2NH3, CaCb dNHs, and CaCb SNHs. 

Fluoromethyl phenyl sulfone, 135 Chlorohydrins Calcium borohydride, 62 Lithium, 157 Sodium nitrite, 282 Titanium(IV) chloride-1,8-Diazabi-cyclo[5.4.0]undecene-7, 309 Iodohydrins... 

The lactone function in the bicyclic cyclopentane-lactones can be reduced to a hydroxymethyl group using sodium or calcium borohydride, whereby carbahexo- and -pentofuranoses were obtained (36,37) (Scheme 14). 

Hydride donors, such as calcium borohydride, reduce compound (189) to 2-benzamidocin-namyl alcohol, PhCH=CH(NHCOPh)CH2OH. 

Irradiation of the 5,7-diene gave the previtamin, which was isomerized and saponified to give la-hydroxy-vitamin D3. For the last synthesis of la-hydroxy-7-dehydrocholesterol recorded here, cholesta-l,4,6-triene-3-one was again used as starting steroid.122 Deconjugation of this trienone with strong base followed by immediate reduction with calcium borohydride led to the unstable 3/3-hydroxycholesta-l,5,7-triene which, without isolation, was converted into the 1,4-addition product (265) upon reaction with 4-phenyl-l,2,4-triazoline-3,5-dione. 

S-Benzyl-y-butyrolactones (44) for which convenient preparative procedures are available, and improved techniques for their a-alkylation and a-hydroxyalkylation, provide the most common synthetic route for these lignan sub-classes (39). The Stobbe condensation (40) of aryl aldehyde with dimethyl succinate (Scheme 9) leads to the half-ester (42) which can be catalytically hydrogenated at atmospheric pressure to give the dihydro half-ester (43). Selective reduction of the potassium salt of the latter can be effectively achieved by calcium borohydride (41)... 

Calcium borohydride is generated in methanol or ethanol from CaCl2 and NaBH [BR3]. It reduces esters to alcohols, leaving acid salts intact, thus allowing the formation of lactones from hemiesters [LRl] (Section 3.2.5). It has also been used in stereoselective reduction of a,p-epoxyketones [TF2] (Section 3.2.4). 

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