Reduction reagents

In contrast there are many examples for reduction processes on polymeric supports, because it is an especially useful transformation for aromatic nitro compounds in solid-phase chemistry. The reaction can be divided into two general classes polymer-bound substrates and polymer-bound oxidant- and reductant-reagents. 

The correlation tables on the following pages show how the main types of compounds are reduced to various products by different reducing agents. The tables list only the reactions contained in this book (with exceptional cases omitted). If a reagent for a certain conversion is not listed, that does not necessarily mean that it cannot accomplish a particular reduction. Reagents listed in parentheses apply only under special conditions or are used exceptionally. 

The 1,2,3,4-isomer is also the major product if other reduction reagents [7] such as anhydrous hydrazine [6], diimide [3] or palladium hydride wrapped in gold foil [15] are used. Contrary to this result, reduction with wet Zn/Cu couple (Section 5.2.2) does not lead to the cis-l-adduct. Instead the e-isomer and the trans-3-isomer are formed as major products [5]. 

Reductant A solution of 1% w/v sodium borohydride (NaBHJ should be freshly prepared in 0.1 M sodium hydroxide (NaOH), and placed in the reductant reagent compartment of the PS Analytical continuous flow hydride generator. 

Synthesis methodology is expanded to cover a range of new reagents, including oxidants and reductants reagents for asymmetric synthesis and those derived from lithium, boron, silicon, phosphorus and sulphur. 

REDUCTION, REAGENTS Aluminum amalgam. Borane-Dimethyl sulfide. Borane-Tetrahydrofurane. t-Butylaminoborane. /-Butyl-9-borabicyclo[3.3.1]nonane. Cobalt boride— f-Butylamineborane. Diisobutylaluminum hydride. Diisopropylamine-Borane. Diphenylamine-Borane. Diphenyltin dihydride. NB-Enantrane. NB-Enantride. Erbium chloride. Hydrazine, lodotrimethylsilane. Lithium-Ammonia. Lithium aluminum hydride. Lithium borohydride. Lithium bronze. Lithium n-butylborohydride. Lithium 9,9-di-n-butyl-9-borabicyclo[3.3.11nonate. Lithium diisobutyl-f-butylaluminum hydride. Lithium tris[(3-ethyl-3pentylK>xy)aluminum hydride. Nickel-Graphite. Potassium tri-sec-butylborohydride. Samarium(II) iodide. Sodium-Ammonia. Sodium bis(2-mcthoxyethoxy)aluminum hydride. 

Figure 7.1. Flow diagram of the system for determination of manganese. P peristaltic pump S injection port R reaction coil (length 30 cm) M mixing coil (length 60 cm) and W waste. The numbers in the pump are the flow rates in ml/min of the carrier, reduction, reagent, neutralisation and masking streams, which correspond to (a), (b), (c), (d) and (e), respectively. The distances S-C and C-B are approximately 2 cm. From [29]...

Use of Ph3P and (AlkO)3P for the transformation of 1,2,4-dithiazole derivatives is described in Section 6.03.5.3 and in CHEC(1984) <1984CHEC(6)897>. In addition to structures containing trivalent phosphorus, other reductive reagents (e.g., NaBH4) are also employed for the 1,2,4-dithiazole ring transformation <1996CHEC-II(4)453>. 

Besides electrophiles and nucleophiles, several linkers are designed to be cleaved by oxidative or reductive methods (Tables 6.1.5 and 6.1.6). Besides the feature of orthogonality with other cleaving methods, a drawback in the use of oxidative or reductive reagents is the need to remove excess reagents or by-products. 

Bu3SnH cannot generally be used for radical alkylation of heteroaromatics, since it is a reductive radical reagent. However, O-acyl esters (2) are not a reductive reagent. 

Thiadiazolidines cannot be prepared by catalytic or chemical reductions. Reagents vigorous enough to reduce the double bonds in a 1,2,4-thiadiazole ring also cleave the ring (see Section 4.25.3.1.8). No other synthesis of 1,2,4-thiadiazolidines has been reported. 

Fig. 5.13 Electrochemical oxime reduction. Reagents and conditions divided cell, BDD/Nb cathode, 1% NaOCH3 in anhydrous MeOH, 40°C, 3.4 Adm-2,4 h, yield = 96% (by GC)...

NAD A Coenzyme Nicotinamide adenine dinucleotide (NAD) is one of the principal oxidation-reduction reagents in biological systems. This nucleotide has the structure of two D-ribose rings (a dmucleotide) linked by their 5 phosphates. The aglycone of one ribose is nicotinamide, and the aglycone of the other is adenine. A dietary deficiency of nicotinic acid (niacin) leads to the disease called pellagra, caused by the inability to synthesize enough nicotinamide adenine dinucleotide. 

REDUCTION, REAGENTS Bis(N-methylpi-perazinyl)aluminum hydride. Borane-Di-methyl sulfide. Borane-Tetrahydrofurane. Borane-Pyridine. n-Butyllithium-Diisobu-tylaluminum hydride. Calcium-Amines. Diisobutylaluminum hydride. 8-Hydroxy-quinolinedihydroboronite. Lithium aluminum hydride. Lithium 9-boratabicy-clo[3.3.1]nonane. Lithium n-butyldiisopro-pylaluminum hydride. Lithium tri-j c-butylborohydride. Lithium triethylborohy-dride. Monochloroalane. Nickel boride. 2-Phenylbenzothiazoline. Potassium 9-(2,3-dimethyl-2-butoxy)-9-boratabicy-clo[3.3.1]nonane. Raney nickel. Sodium bis(2-methoxyethoxy)aluminum hydride. Sodium borohydride. Sodium borohy-dride-Nickel chloride. Sodium borohy-dride-Praeseodymium chloride. So-dium(dimethylamino)borohydride. Sodium hydrogen telluride. Thexyl chloroborane-Dimethyl sulfide. Tri-n-butylphosphine-Diphenyl disulfide. Tri-n-butyltin hydride. Zinc-l,2-Dibromoethane. Zinc borohydride. 

The author believes that students are well aware of the basic reaction pathways such as substitutions, additions, eliminations, aromatic substitutions, aliphatic nucleophilic substitutions and electrophilic substitutions. Students may follow undergraduate books on reaction mechanisms for basic knowledge of reactive intermediates and oxidation and reduction processes. Reaction Mechanisms in Organic Synthesis provides extensive coverage of various carbon-carbon bond forming reactions such as transition metal catalyzed reactions use of stabilized carbanions, ylides and enamines for the carbon-carbon bond forming reactions and advance level use of oxidation and reduction reagents in synthesis. 

REDUCTION, REAGENTS Bis(triphenyl-phosphine)copper tetrahydroborate. Borane-Pyridine. Calcium-Methylamine/ ethylenediaminc. Chlorobis(cyclopenta-dienyl)tetrahydroboratozirconium(IV). Chromium(II)-Amine complexes. Copper(0)-lsonitrile complexes. 2,2-Dihydroxy-l, 1-binaphthyl-Lithium aluminum hydride. Di-iododimethylsilane. Diisobutyl-aluminum 2,6-di-/-butylphenoxide. Diisobutyl aluminum hydride. Dimethyl sulfide-Trifluoroacetic anhydride. Disodium tetracarbonylferrate. Lithium-Ammonia. Lithium-Ethylenediamine. Lithium bronze. Lithium aluminum hydride. Lithium triethylborohydride. Potassium-Graphite. 1,3-Propanedithiol. Pyridine-Sulfur trioxide complex. 

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