Sodium borohydride -Cobaltous chloride

Beccalli et al. reported a new synthesis of staurosporinone (293) from 3-cyano-3-(lH-indol-3-yl)-2-oxo propionic acid ethyl ester (1464) (790). The reaction of 1464 with ethyl chlorocarbonate and triethylamine afforded the compound 1465, which, on treatment with dimethylamine, led to the corresponding hydroxy derivative 1466. The triflate 1467 was prepared from 1466 by reaction with trifluoromethanesulfonic anhydride (Tf20) in the presence of ethyldiisopropylamine. The palladium(O)-catalyzed cross-coupling of the triflate 1467 with the 3-(tributylstannyl)indole 1468 afforded the vinylindole 1469 in 89% yield. Deprotection of both nitrogen atoms with sodium ethoxide in ethanol to 1470, followed by photocyclization in the presence of iodine as the oxidizing agent provided the indolocarbazole 1471. Finally, reductive cyclization of 1471 with sodium borohydride-cobaltous chloride led to staurosporinone (293) in 40% yield (790) (Scheme 5.248). 

The reduction of the nitro group at C-2 of the thiodisacharides was efficiently carried out with sodium borohydride/cobalt chloride complex, followed by conventional acetylation. Final deprotection by ring opening was accomplished by the treatment with p-toluenesulfonic acid in methanol solution followed by deacetylation with aqueous/methanol solution containing catalytic amount of triethylamine. 

The reduction of the C-a-nitro function of new nitro-S-thiodisaccharide was performed in the same fashion as described by us earlier (3) with sodium borohydride/cobalt chloride complex. For the purpose of purification and isolation, the corresponding amino derivatives were acetylated in situ and selectively deprotected to free amino derivatives at C-2 by employing Hanessian methodology 26) using triethyloxonium fluoroborate. 

Reduction. Nitriles and amides are not reduced by sodium borohydride alone but are reduced to primary amines in satisfactory yields by the combination of sodium borohydride-cobaltous chloride in both hydroxylic and nonhydroxylic solvents.1 Aromatic nitro compounds are reduced by this system to azoxy com-... 

The numbers in parentheses are corrected for 92% ee a-pinene. Sodium borohydride-cobaltous chloride reduction is performed as soon as the reduction of carbonyl is complete. Warming of the reaction mixture or longer times leads to the formation of undesired product... 

The azidohydrins obtained by azide ion opening of epoxides, except for those possessing a tertiary hydroxy group, can be readily converted to azido mesylates on treatment with pyridine/methanesulfonyl chloride. Reduction and subsequent aziridine formation results upon reaction with hydrazine/ Raney nickel, lithium aluminum hydride, or sodium borohydride/cobalt(II)... 

Lithium acetyl(carbonyl)nitrosyltris-(triphenylphosphine)cobaltate, 102 Sodium borohydride-Cobalt(II) chloride, 249... 

Silver(I) acetate, 396 Silver hexafluoroantimonate, 467 Silver imidazolate, 467 Silver nitrite-Mercury(II) chloride, 467-468 Silver(l) oxide, 468-469 Silver(II) oxide, 469 Silver perchlorate, 469-470 Silver tetrafluoroborate, 471 Silver(I) trifluoracetate, 471 Simmons-Smith reagent, 210-211, 472, 598 Sinularene, 246 Slaframine, 114, 115 Sodium amalgam, 473-475 Sodium-Ammonia, 472 Sodium benzeneselenoate, 475 Sodium bicarbonate, 476 Sodium bis(methoxyethoxy)aluminum hydride, 93, 476-477 Sodium borate, 322 Sodium borohydride, 477-479, 499 Sodium borohydride-Cobalt(IF) chloride, 479 Sodium borohydride-Methanesulfonic acid,... 

Primary Amines.—The aromatic nitro-to-amine conversion has figured prominently in the current literature/ with the emphasis once again on selectivity. Thus, sodium borohydride-stannous chloride, lithium cobalt(i)... 

It was shown that dibenzothiophene oxide 17 is inert to 1-benzyl-l,4-dihydro nicotinamide (BNAH) but that, in the presence of catalytic amounts of metalloporphyrin, 17 is reduced quantitatively by BNAH. From experimental results with different catalysts [meso-tetraphenylporphinato iron(III) chloride (TPPFeCl) being the best] and a series of substituted sulfoxides, Oae and coworkers80 suggest an initial SET from BNAH to Fe1 followed by a second SET from the catalyst to the sulfoxide. The results are also consistent with an initial coordination of the substrate to Fem, thus weakening the sulfur-oxygen bond in a way reminiscent of the reduction of sulfoxides with sodium borohydride in the presence of catalytic amounts of cobalt chloride81. 

The boride precipitated from sodium borohydride and cobalt(II) chloride in methanol becomes pyrophoric after vacuum drying. It can safely be stored solvent-moist. 

A combination of chiral cobalt-catalyst and sodium borohydride was successfully applied to the asymmetric reduction of aromatic ketones. A chiral cobalt complex 164 (5 mol%), prepared from the corresponding salen-type chiral bisketoaldimine and cobalt(II) chloride, catalyzed the reduction of dimethylchromanone 165 in the presence of sodium borohydride (1.5 equiv to ketone) in chloroform, including a small amount of ethanol at -20°C for 120 h to give alcohol 166 92% ee (S ) in 94% yield (Scheme 2.18) [94], Addition of tetrahydrofurfuryl alcohol (THFFA) to the reaction system or the use of pre-modified borohydride, NaBH2(THFFA)2, improved the catalyst activity, that is, using this protocol, the reactions of ketone 165 and... 

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