Sodium borohydride-manganese

A number of pendant arm ligand derivatives based on hexamine macrocyclic backbones have been reported." One such species was formed by the [2 -f 2] Schiff base condensation between 3,3-iminobis(propylamine) and diformyl-p-cresol followed by sodium borohydride reduction of the four imine functions so generated. Potentiometric studies indicate that a range of both mononuclear and dinuclear species are formed in solution with manganese(II) incorporating various both protonated and nonprotonated forms of the ligand. 

The structure of the methyl ester m.p. 174° C. (XL) was proven (5) mainly by the fact that the corresponding dibasic acid (XLI R = H) and its dimethyl ester (XLI R = Me) are oxidized with periodate and that the dimethyl ester is oxidized by manganese dioxide to a trisubstituted a,/ -unsaturated ketone (XLII) which regenerates (XLII R = Me) with sodium borohydride. 

The synthesis of 3-hydroxy-2-methyl esters and amides in a stereoselective manner is a challenge which needs to be met due to the prevalence of these moieties in natural products201. This has been accomplished by using sodium borohydride, catalyzed by manganese(II) chloride or by tetrabutylammonium borohydride (equation 52)202,203. 

Dihydrothieno[3,4-d]pyrimidin-3(l//)-ones 337 were synthesized by a four-step reaction sequence starting from carbamates 310. The latter were selectively reduced with lithium aluminum hydride and then oxidized with activated manganese(IV) oxide to give aldehydes 334 in one-pot. Condensation of compounds 334 with ethanolamine in refluxing ethanol afforded the Schiff bases 335, which were reduced with sodium borohydride to... 

Acetylpyridazine and pyridazine-4-carbaldehyde are reduced with sodium borohydride to the corresponding carbinols (299 R = H or Me). ° Pyrid-azine-4-carbaldehyde (228 R = H) is prepared by oxidation of 4-styryl-pyridazine (227), obtained by condensation of 4-methylpyridazine with benzaldehyde." A similar procedure can be applied to prepare the 3-aldehyde, which can be obtained also from the corresponding carbinol by oxidation with manganese dioxide. With sodium in liquid ammonia under Birch reduction conditions halopyridazines are dehalogenated. ° ... 

Oxidation of both carbinols 160a and 160b with manganese dioxide afforded the ketone 162 which was reduced with sodium borohydride to give a mixture of compounds 160a and 160b, thus proving that they are stereoisomers. The formation of these products is rationalized in terms of a radical intermediate as shown in Chart 37. 

Partial hydrolysis of 0,0-diacetyl-0-methylgolceptine gave a monoacetyl derivative that was oxidized by manganese dioxide to an a, -unsaturated ketone. Reduction of this ketone with sodium borohydride gave 0-methylgolceptine and a C-2 epimer. The latter formed an isopropylidene derivative (70). 

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