Sodium borohydride halides, tertiary

The reagent is prepared by reaction or toluene with hexane, ng agent comparable to other lithium VC 1,2-rcduction of enoncs. Reduction proceeds at —78°. However, ketones cr. Esters arc reduced to a mixture of in alcohol can be effected by reduction sodium borohydride. Tertiary amides Ics in generally high yield. Selective ondary halides is possible. 

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. 

Reduction of tertiary kaiides. Tertiary halides are reduced to hydrocarbons by. sodium borohydride in tetramethyicne sulfone (sulfolane, 1, 1144-1145 2, 402 -403). The reaction proceeds by way of elimination, hydroboration, and protonolysis. Halides... 

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. 

Halides. Sodium borohydride reduces secondary and tertiary alkyl halides capable of forming relatively stable carbonium ions, for example benzhydryl... 

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... 

Methods reported this year for the reduction of alkyl halides to alkanes include the potassium-dicyclohexyl-18-crown-6 reduction of alkyl fluorides, sodium borohydride reduction of alkyl chlorides, bromides, and iodides (or sulphonate esters) under liquid-liquid phase-transfer conditions, and the selective reduction of tertiary alkyl, benzyl, and allyl halides with the borate (61). Continuing... 

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]. 

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