Sodium cyanoborohydride-Zinc chloride

Ketoester 208 derived from l-(2-nitrophenyl)-lH-pyrrole and ethyl oxalyl chloride can be selectively reduced at the keto group with zinc iodide and sodium cyanoborohydride. Further reduction of the nitro group and cyclization to lactam 209 has been accomplished by treatment with stannous chloride in refluxing ethanol (Scheme 43 (2003BMCL2195)). 

Tributyltin hydride, 316 Zinc iodide, 280 From alkyl halides Lithium aluminum hydride-Ceri-um(III) chloride, 159 Palladium catalysts, 230 Sodium cyanoborohydride-Tin(II) chloride, 280 From alkyl sulfonates Lithium triethylborohydride, 153 From thiols... 

Sodium borohydride-Palladium chloride. Sodium borohydride-Rhodium(lII) chloride. Sodium borohydride-Tin(II) chloride. Sodium cyanoborohydride. Sodium 9-cyano-9-hydrido-9-borabicyclo[3.3.1]nonane. Sodium dithionite. Sodium hydride-Sodium t-amyl oxide-Zinc chloride. Sodium trimethoxyborohydride. Tetra-/i-butylammonium borohydride. Tetra-n-butylammonium cyanoborohydride. Tetra-n-butylammonium octahydrotriborate. Tri-n-butyltin hydride. Triethoxy silane. Triisobutylaluminum-Bis(N-methyl-salicyclaldimine)nickel. Zinc borohydride. REDUCTIVE CYCLIZATION Cobaloximc(I). 

A mixture of sodium cyanoborohydride (0.11 mmol) and zinc chloride (0.05 mmol) in 2 ml methyl alcohol was added to a solution containing the Step 2 product (0.05 mmol) and 4-(4-fluorophenyl)piperidine (0.05 mmol) dissolved in 2 ml methyl alcohol, then stirred overnight at ambient temperature. The mixture was concentrated and the residue treated with 3 ml saturated NaHC03 solution and 5 ml CH2C12. The layers were separated and the organic component poured into an SCX cartridge, then washed four times with 2 ml methyl alcohol. It was then eluted twice with 2 ml 2 M methyl alcohol/ammonia, concentrated, and the product was isolated in 70% yield as a colorless solid. 

Fentanyl and its analogs are made from TV-substituted-4-piperidones [i.e., from the same intermediates of the reversed esters of pethidine (p. 266)]. These ketones condense with aniline under the influence of catalysts such as toluene-p-sulfonic acid(2) and zinc chloride(18) to give Schiff bases, which are reduced to diamines 4 by NaBH4 or LAH. Recently, the direct conversion of 4-piperidones to 4-anilino derivatives 4 has been achieved by reductive amination with aniline and sodium cyanoborohydride (NaBH3CN).(19) The diamines are acylated with propionic anhydride. 

Zinc-modified cyanoborohydride, prepared from anhydrous zinc chloride and sodium cyanoborohy-dride in the ratio 1 2 in ether, selectively reduced aldehydes and ketones but not acids, anhydrides, esters and tertiary amides. In methanol the reactivity paralleled the unmodified reagent. Zinc and cadmium borohydrides form solid complexes with DMF, which may prove to be convenient sources of the reducing agents.Aromatic and a,p-unsaturated ketones were reduced much more slowly than saturated ketones, so chemoselective reduction should be possible. 

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). ... 

Selective reduction of either the pyridine or the benzene rings in quinolines and isoquinoline can be achieved the heterocyclic ring is reduced to the tetrahydro level by sodium cyanoborohydride in acid solution,by sodium borohydride in the presence of nickel(II) chloride, by zinc borohydride," or, traditionally, by room temperature and room pressure catalytic hydrogenation in methanol. However, in strong acid solution it is the benzene ring which is selectively saturated " longer reaction times can then lead to decahydro-derivatives. 

Sodium cyanoborohydride modified with zinc chloride will reduce... 

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