Sodium borohydride halides, primary

A one-pot PTC reaction procedure for the overall conversion of an alkyl halide into a primary amine via an azide is particularly illustrative.204 Thus the reduction of the azide is effected by the addition of sodium borohydride to a reaction mixture arising from the PTC displacement reaction of an alkyl halide with sodium azide (the preparation of 1-octylamine, Expt 5.193). The reaction appears to be applicable to primary and secondary alkyl halides, alkyl methane-sulphonates and benzylic halides. 

Reductions. This hydride is a strong reducing agent comparable to other lithium trialkylhydrides. It is superior to DIBAH for selective 1,2-reduction of enones. Reduction of ketones, esters, acid chlorides, and anhydrides proceeds at -78°. However, ketones can be reduced selectively in the presence of an ester. Esters are reduced to a mixture of an alcohol and an aldehyde. Complete reduction to an alcohol can be effected by reduction at -78° with 2 equiv. of 1 and then with excess sodium borohydride. Tertiary amides are reduced by 1 equiv. of the reagent to aldehydes in generally high yield. Selective reduction of primary halides in the presence of secondary halides is possible. 

Sodium borohydride, a representative borohydride reagent, behaves as an effective source of nucleophilic hydride in an aprotic polar solvent, such as DMSO, sulfolane, HMPA, DMF or diglyme, and is used for the reduction of alkyl halides. As shown in Table 3, primary and secondary iodides, bromides and chlorides are converted to hydrocarbons at temperatures between 25 and 100 C using sodium borohydride. Vicinal dihalides, such as 1,2-dibromooctane, are smoothly converted to the corresponding saturated hydrocarbons, in contrast to the reductions using LiAlH4 or low-valent metal salts, which predominantly afford alkenes. 

Some alkyl halides (primary I, Br, Cl and secondary Br) are reduced by NaBH4 under phase-transfer conditions, as shown in equation (4). This reaction is carried out by the addition of a concentrated aqueous solution of NaBH4 to a stirred solution of substrate and catalyst in a suitable solvent, such as toluene. Yields are nearly quantitative in most cases, although an excess of sodium borohydride is required. 

A zinc-modifled cyanoborohydride reagent, prepared in situ by the reaction of sodium borohydride with zinc chloride in ether, reduces tertiary halides in high yields, whereas primary and secondary halides remain intact. Similar reactivity is observed with lithium 9,9-di-n-butyl-9-borabicyclo[3.3.1]-nonanate (4), as shown in equation (5). ... 

Reduction of alkyl halides. LiAlH, is satisfactory for reduction of primary and secondary halides or tosylates to the hydrocarbons, but in the case of a tertiary halide the product is predominantly the olefin. Alkyl halides and tosylates, even tertiary, are reduced in good to high yield by sodium borohydride in 65% aqueous diglyme. When a relatively stable carbonium ion incapable of elimination is formed, yields are high, but yields are still satisfactory when elimination is possible. The reaction is very slow in the absence of water. A homogeneous solution required for kinetic studies is prepared from 80% (volume) aqueous diglyme, which can be made 1.80 M in the reagent. 

Reduction of halides. Primary, secondary, and certain tertiary halides and tosylates can be selectively reduced by sodium borohydride in DMSO or sulfolane. 1,2-Dibromides are reduced to hydrocarbons in moderately good yields. The method complements that of Bell and Brown,2 which uses sodium borohydride in 65% aqueous diglyme for reduction of secondary and tertiary alkyl halides which are capable of forming relatively stable carbonium ions (1, 1054). Lithium aluminum hydride reduction affords only olefins. Reduction of optically active tertiary alkyl halides proceeds with racemization, presumably by way of an elimination-addition mechanism.3... 

Fragmentations of heterocycles have played an important role in the preparation of amide derivatives. Moderate to good yields of a-hydroxy-amides were obtained on reaction of a-hydroxy-acid aceto-nides with primary amines.N-Alkyl-2-methyl-2-oxazolinium salts (obtained by mixing alkyl halides and 2-methyl-2-oxazoline in dichloromethane) were found to react with sodium benzeneselenolate to yield -(2-phenylselenoethyl)-t -alkylacetamides, which after oxidation to ] -vinyl analogues with sodium metaperiodate in methanol, gave secondary amides on sequential treatment with mercuric acetate in aqueous tetrahydrofuran and sodium borohydride/3M... 

General Synthesis and Reactions.—Linear primary alcohols with at least seven carbon atoms are transformed into esters in high yield using copper oxide at temperatures above 170 C in the liquid phase. RusfCO) catalyses the conversion of an aldehyde, or an alcohol with the same number of carbon atoms, into an ester in the presence of diphenylacetylene. " The carbonylation of organic halides in the presence of cyclic ethers is catalysed by PhPdI(PPh3)2 , it provides a synthesis of halohydrin esters in reasonable yield. Cyanohydrin esters have been synthesized by the sodium borohydride reduction of acyl cyanides in the presence of tetra-n-butylammonium bromide. ... 

Aldehydes can be alkylated indirectly via the corresponding imines lithium dialkylamides readily deprotonate such imines at the position a to the azomethine group, and the carbanions formed can be alkylated with primary halides. This route to a-substituted aldehydes avoids the use of sodium borohydride, necessary in the dihydro-1,3-oxazine alternative. 

Reactions.— DMF is recommended as solvent for the sodium borohydride reduction of primary and secondary alkyl halides to the corresponding hydrocarbons this reaction, which proceeds at room temperature, shows the kinetic behaviour of an 5 fj2 process. The intermediacy of organoboranes in the analogous reduction of tertiary halides has been demonstrated "... 

SO an excess is used to minimize this. A secondary or tertiary amine may be prepared by treating a primary or secondary amine with an alkyl halide or sulfonate in the same way. Primary amines can be made cleanly using potassium phthalimide instead of ammonia, and a number of improvements to the original procedure have been suggested. Osby and co-workers have treated the phthalimide with sodium borohydride and propanol followed by acetic acid to isolate the primary amine in high yield [92]. 

NaBHi in polyethylene glycols." NaBH, in PEG, particularly PEG 400, is more reactive than NaBH4 in the usual hydroxy lie solvents, possibly because a sodium dialkoxy-borohydride is generated. This system reduces esters and acyl chlorides to primary alcohols, and halides or tosylates to hydrocarbons. 

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