Potassium borohydrides, derivatives

Reaction of vindoline (3) with the chloroindolenines derived from vin-cadifformine (127a), iJ -vincadifformine (133), -tabersonine (133a), or synthetic pandoline (34) (7/5, 116), followed by reduction of the resulting imines 145 and 145a (Scheme 40) with potassium borohydride, had given... 

Reaction of the imine-indoline products 157 and 158 with potassium borohydride in acetic acid resulted in rupture of the C-3 -C-7 bond and reduction of the resulting imonium function (Scheme 45). While the initial C-I6 -C-14 PARF imine-indolines 157 and 158 can be isolated, they are less stable on silica gel chromatography than the corresponding l -vincad-ifformine-derived C-16 -C-14 PREF compounds 145, and consequently purification of the vindoline coupling products and separation of dia-stereomers were best carried out at the indole-indoline stage (162, 163). 

Conversion of the resulting separate D-seco D-E trans i-vincadiffor-mine diols 198-201 to their primary tosylates and tertiary trimethylsilyl-oxy derivatives 202-205 and coupling to vindoline by the chlorination-silver tetrafluoroborate-potassium borohydride sequence provided amino tosylates 206-209, which could be directly subjected to cyclization or, alternatively, converted to the C-20 -C-21 epoxides 178, 181, 210, and 211 by reaction with tetrabutylammonium fluoride (Scheme 53). While cyclization of the tosylates 206-209 led essentially only to quaternary salts which could be debenzylated to provide the lower energy atropi-somer of vinblastine (1), leurosidine (56), vincovaline (184), and its C-20 epimer (212) respectively, cyclization of the epoxides 178, 181, 210, and... 

The pyridine ring is easily reduced in the form of its quaternary salts to give hexahydro derivatives by catalytic hydrogenation [446], and to tetrahydro and hexahydro derivatives by reduction with alane aluminum hydride) [447], sodium aluminum hydride [448], sodium bis 2-methoxyethoxy)aluminum hydride [448], sodium borohydride [447], potassium borohydride [449], sodium in ethanol [444, 450], and formic acid [318]. Reductions with hydrides give predominantly 1,2,5,6-tetrahydro derivatives while electroreduction and reduction with formic acid give more hexahydro derivatives [451,452]. 

Bobowsky and Shavel found an interesting intramolecular reductive transacylation reaction, in which substituted cyclopent[e][l,3]oxazin-2-ones and l,3-perhydrobenzoxazin-2-ones (90) were formed (80JHC277). In the reactions of 4-(2 -oxocycloalkyl)-3,4-dihydro-3-methyl-2//-l,3-benzoxazin-2-ones 88 and potassium borohydride, the 2 -hydroxycycloalkyl products 89 obtained underwent intramolecular transacylation reactions, resulting in the dihydro-1,3-oxazine derivatives 90. In this way, the 4-(2 -oxocycloalkyl)... 

Figure 7 Crystal structures of (a) uncomplexed [2.2.2]cryptand (12) (b) potassium complex of [2.2.2]cryptand (c) bis-borohydride derivative of [2.2.2]cryptand (reproduced with permission from 76JCS(P2)423 and 73AX(B)383)...

Oxo-groups located at other positions on the pteridine ring were shown by Albert and Matsuura152 to affect the structure of the dihydropteridine formed. Thus, pteridin-4- and 6-ones and 2,6- and 4,6-diones were converted to the corresponding 7,8-dihydro-derivatives (153), whereas pteridin-7-one and 4,7-dione formed the corresponding 5,6-dihydro-derivatives (154) on reaction with potassium borohydride. 

Whenever the formation of the chano form was allowed, the appropriate consequences were observed (1), e.g., formation of cfomoajmaline oxime, mp 220°, and from it by dehydration the corresponding nitrile, mp 254°-255°, [a]D + 29° (CHCI3) Wolff-Kishner reduction of ajmaline to deoxydihydrocforooajmaline, mp 185°-186°, [a]D + 39° (CHCI3) reduction of ajmaline with potassium borohydride to furnish dihydro-cfccmoajmaline, mp 200° (34) formation of 21-alkylaminoisoajmaline derivatives by heating ajmaline with primary amines (35) and epi-merization of ajmaline in the presence of alkali to the more stable isomer isoajmaline (1). 

Reduction with concomitant A, Af -dialkylation is achieved by the action of potassium borohydride in the presense of carboxylic acids. Similarly, reduction of quinoxalines with sodium borohydride or sodium cyanoborohydride in the presence of benzyl chloroformate gives A -benzyloxycarbonyl- or /V,jV -bis(benzyloxycarbonyl)tetrahydro derivatives. ... 

The nucleus of indazole, like that of pyrazole, is stable to reduction, so that treatment of the amido derivative (23) with LAH leads only to the amine (24).Indazolium salts (25) are more reactive and undergo reduction with potassium borohydride to give indazolines (26). ... 

Chromatographic methods have also been developed for quantitative determination of the AUC of pectin. Uronic acids have been analyzed using gas-liquid chromatography (GLC) after conversion to L-galactono-1,4-lactone via potassium borohydride reduction and lactonization using methanolic hydrogen chloride. The derived lactone was then analyzed by GLC as the trimethylsilyl derivative (Perry... 

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. 

Lithium aluminum hydride reduces 2,3-dimethylpyrido[3,4-h]pyrazine to the cis-tetrahydro derivative, analogous to that described in the pyrido[2,3-h]pyrazine series. Potassium borohydride has been used to reduce the oxo compound 79 to the tetrahydro derivative 80." ... 

Reduction of the most unsaturated rings is dealt with first. Dihydropyridopyrazines (91) are reduced by sodium or potassium borohydride <815481,81URP798104,86ZOR2610> or by hydrogen with palladium catalysts or LAH <80GEP(O)2832488> to the tetrahydro derivatives (92) quaternary salts... 

Lynestrenol is the des-3-oxo derivative of norethindrone (28). It has been prepared through a similar synthetic pathway as aHylestrenol (37) (52), ie, addition of potassium acetyUde, rather than aHyl magnesium bromide, affords lynestrenol (73). Lynestrenol is also available from norethindrone (28). Reduction of the 3-keto group is accompHshed by treating norethindrone (28) with sodium borohydride in the presence of trifluoro- or trichloroacetic acid... 

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