Diethyl reduction with sodium borohydride

Condensation of 4,4-dithiobis(benzoic acid) (38) [52] with diethyl L-glutamate in the presence of DCC produced (39), from which (40) was readily obtained by reduction with sodium borohydride [53] (Scheme 3.7). 

In preparation for the eventual removal of the undesired oxygen function at C-10 of 313 via a Birch reduction, the phenol 313 was phosphorylated with diethyl phosphorochloridate in the presence of triethylamine to give 314, which underwent stereoselective reduction with sodium borohydride with concomitant N-deacylation to deliver the amino alcohol 315. N-Methylation of 315 by the Eschweiler-Clarke protocol using formaldehyde and formic acid followed by ammonolysis of the ester group and acetylation of the C-2 hydroxyl function afforded 316. Dehydration of the amide moiety in 316 with phosphorus oxychloride and subsequent reaction of the resulting amino nitrile 317 with LiAlH4 furnished 318, which underwent reduction with sodium in liquid ammonia to provide unnatural (+)-galanthamine. 

Toward this end, exposure (9 h) of dienophile (284) to 5.0 equiv. of dienoic acid (285) in 3.0 M LiClOr-diethyl ether gave rise in 72% yield to crystalline keto acid (286), a which was reduction with sodium borohydride in methanol at 0°C by treatment with concentrated hydrochloric acid afforded the crystalline tetracyclic alcohol (287). To set the stage for the inversion of configuration at C(9), tetracyclic alcohol (287) was transformed into tetracyclic enone (291), via tetracyclic ketone (290), which was readily available by a five-step sequence from (287) described above [133],... 

The reduction of diethyl Af-(4-methylpiperazin-l-yl)methylenemalonate over a platinum catalyst with hydrogen or with sodium borohydride af-... 

Nickel prepared by reduction of nickel chloride with sodium borohydride was used for desulfurization of diethyl mercaptole of benzil. Partial desulfurization using 2 mol of nickel per mol of the mercaptole gave 71% yield of ethylthiodesoxybenzoin while treatment with a 10-fold molar excess of nickel over the mercaptole gave 61% yield of desoxybenzoin (benzyl phenyl ketone) 937. ... 

Reduction of 5-methyl-l,3,4,6,ll,lla-hexahydro-2//-pyrimido[l,2-b]-isoquinolinium iodides (43) with LAH in diethyl ether (R = H) or with sodium borohydride in water (R = Me) yielded 1,2,3,4,5,6,7,8-octahydro-2-methyl-2,6-benzodiazecines (44) (73JOC437). 

In order to transform the spirocyclic enone 445 to ( )-elwesine (439) and ( )-epielwesine (449), it was treated with boron trifluoride and dimethylsulfide to cleave the Al-carbobenzyloxy protecting group, and cyclization of the resulting amino enone spontaneously ensued to produce ( )-dihydrooxocrinine (447). Reduction of carbonyl function of 447 with sodium borohydride afforded ( )-3-epielwesine (449), which was converted to ( )-elwesine (439) by inversion of the hydroxyl function at C-3 via a Mitsunobu protocol using diethyl azodicarboxylate, triphenylphosphine, and formic acid. Attempted reduction of 447 directly to 439 by a Meerwein-Ponndorf-Verley reduction or with bulky hydride reagents gave only mixtures of 449 and 439 that were difficult to separate. 

Dilithium or disodium areneditellurolates were alkylated with methyl iodide3, dimethyl sulfate4, or diethyl sulfate4. The areneditellurolates were prepared from the corresponding dibromides and tert.-butyl lithium in tetrahydrofuran and treatment of the resulting mixture with powdered tellurium3, or by the reduction of poly(l,4-phenylene ditellurium) with sodium borohydride in ethanol/benzene4. 

Some years ago, Malmstrom etal. synthesized water-soluble metal phosphine complexes based on water-soluble polymers [41], In order to have solubility in both an acidic and a basic medium, they prepared two different water-soluble polymers. For the first, they made methyl [4-(diphenylphosphino)benzyl]amine (PNH) react with poly(acrylic acid) (PAA) using dicydocarbodiimide (DCC) as the coupling agent, under strict exclusion of oxygen (25). For the second, they reacted (4-carboxy-phenyl)diphenylphosphine with polyethylene imine (PEI) at room temperature (26). The reduction by sodium borohydride was made in situ, followed by the addition of methanesulfonic add and diethyl ether. Then, the methanesulfonic salt of phosphinated polyethylenimine was predpitated. 

Acetalization of diethyl (—)-(5, iS)-tartrate (2b) with 463 affords in 87% yield the syrupy 479. Nearly quantitative reduction of the ester groups with sodium borohydride followed by ditosylation of the resulting diol and an intramolecular carbon-carbon coupling furnishes 480. 

Esterification of the ketoacid (39) with diazomethane afforded the ketoester (40). This, on treatment with sodium hydride and diethyl carbonate in 1,2-dimethoxyethane, furnished (41) whose NMR spectrum was rather complicated, probably due to contamination with a small amount of tautomer. Reduction of the free carbonyl group with sodium borohydride led to the formation of alcohol whose tosyl derivative on heating with lithium bromide and lithium carbonate in dimethylformamide gave the diester (42). Its spectroscopic properties were identical with those of the one reported [20]. As the diester (42) has already been converted to warburganal (12), the present route for the diester (42) constitutes a formal total synthesis of warburganal. 

Sodium dithionite in water or aqueous dimethylformamide is an economic, efficient system for the dehalogenation of a-halo-ketones. Other reagents that have been described recently for dehalogenation include iron-graphite (prepared by reduction of ferric chloride with potassium-graphite), sodium 0,0-diethyl phosphorotelluroate, and sodium borohydride in the presence of a catalytic amount of bis(2-thienyl) ditelluride. ... 

The reaction of the aldehyde 174, prepared from D-glucose diethyl dithio-acetal by way of compounds 172 and 173, with lithium dimethyl methyl-phosphonate gave the adduct 175. Conversion of 175 into compound 176, followed by oxidation with dimethyl sulfoxide-oxalyl chloride, provided diketone 177. Cyclization of 177 with ethyldiisopropylamine gave the enone 178, which furnished compounds 179 and 180 on sodium borohydride reduction. 0-Desilylation, catalytic hydrogenation, 0-debenzyIation, and acetylation converted 179 into the pentaacetate 93 and 5a-carba-a-L-ido-pyranose pentaacetate (181). 

Tetracyclic keto ester 467, prepared earlier (253), was treated with the anion of diethyl methoxycarbonylmethylphosphonate in dimethylformamide. The reaction supplied the unsaturated ester 492, which was catalytically hydrogenated to diester 493. Dieckmann condensation of 493 yielded two nonenolizable keto esters (494 and 495), which could be separated by fractional crystallization. Sodium borohydride reduction of 18a-methoxyyohimbinone (494) gave two alcohols (496 and 497) in a ratio of about 10 1 at the same time, reduction of 180-methoxyyohimbinone (495) furnished another two stereoisomeric alcohols (498 and 499) in approximately equal amounts. Demethylation of the four stereoisomers (496-499) resulted in the corresponding 18-hydroxyyohimbines (500-503)... 

Scheme 2 shows Rapoport s synthesis [15]. The cinnamic acid derivative 3 prepared from m-methoxy benzaldehyde [20] was ethylated by diethyl sulfate to give ethyl cinnamate derivative 4, followed by Michael addition with ethyl cyanoacetate to afford compound 5. Compound 5 was converted to lactam 6 by the reduction of the cyano group and subsequent cyclization. Selective reduction of the lactam moiety of 6 was achieved by treatment with trimethy-loxonium fluorob orate followed by sodium borohydride reduction. Amine 8 was obtained by the reductive methylation of amine 7. Amine 8 was converted to compound 9 by methylene lactam rearrangement [21], followed by selenium dioxide oxidation to provide compound 10. Allylic rearrangement of compound 10 and subsequent hydrolysis gave compound 12. The construction of the decahydroisoquinoline structure began with compound 12,... 

---