Triethylsilane-, lithium

Although catalytic hydrogenation is the method most often used, double bonds can be reduced by other reagents, as well. Among these are sodium in ethanol, sodium and rerr-butyl alcohol in HMPA, lithium and aliphatic amines (see also 15-14), " zinc and acids, sodium hypophosphate and Pd-C, (EtO)3SiH—Pd(OAc)2, trifluoroacetic acid and triethylsilane (EtsSiH), and hydroxylamine and ethyl acetate.However, metallic hydrides, such as lithium aluminum hydride and sodium borohydride, do not in general reduce carbon-carbon double bonds, although this can be done in special cases where the double bond is polar, as in 1,1-diarylethenes and in enamines. " °... 

Hydrogenation of the carbon-carbon double bond occurs without alteration of the ester function when citronellyl acetate is treated with 2.5 equivalents of trifluoroacetic acid and two equivalents of triethylsilane in 2-nitropropane.205 The reduced product is obtained in 90% yield after 22 hours at room temperature in the presence of one equivalent of added lithium perchlorate (Eq. 82). The yields are lower in the absence of this added salt. Similar reduction of an unsaturated phenolic chroman derivative occurs to give an 85% yield of product with only the carbon-carbon double bond reduced (Eq. 83).205... 

Reduction of carbonyl to methylene in aromatic ketones was also achieved by (dane prepared from lithium aluminum hydride and aluminum chloride [770], by soditim borohydride in triiluoroacetic acid [841 with triethylsilane in trifluoroacetic acid [555, 777], with sodium in refluxing ethanol [842], with zinc in hydrochloric acid [843] and with hydrogen iodide and phosphorus [227], geiibrally in good to high yields. 

If desired, the mixture of triethylsilane and triethylfluorosi-lane can be reconverted into triethylsilane by reduction with lithium aluminum hydride.5... 

A neat way of preparing96 the system (215) (useful in bufadienolide synthesis) from (214) is illustrated for compound (216). Bromination to (217) followed by dehydrobromination with lithium bromide in DMF gave the dienone (218), which on triethylsilane reduction produced (219) and thence, by condensation with diethyl oxalate, (220). Methylthiotoluene-p-sulphonate in ethanol-potassium acetate now produced (221) whose oxidation with N-chlorosuccinimide in 2% methanolic sulphuric acid gave (223). A previous route to such compounds was by way of the a-acetoxy-ketones (219) but suffers from a low yield at the acetoxylation step, (219) —> (222). 

If other reactive moieties are present a cyclopropanecarbonyl compound can be converted to the corresponding cyclopropylalkane using various conditions. Thus, 3,4-benzotricy-clo[4.3.1.0 ]dec-3-en-2-one yielded 3,4-benzotricyclo[4.3.1.0 ]dec-3-ene in excellent yield on treatment with sodium in liquid ammonia. di-l-Methylcyclopropane-l,2-dicarboxylic anhydride underwent a similar reaction to afford isomeric lactones on treatment with lithium aluminum hydride or sodium borohydride in tetrahydrofuran. On the other hand, ionic hydrogenation (triethylsilane in trifluoroacetic acid and water) of cyclopropyl phenyl ketone gave a complex reaction mixture and very little benzylcyclopropane. ... 

However, this sequence can be reversed. - Thus, the activated cyclopropane can be de-protonated by lithium diisopropylamide, reacted with an appropriate ketone and opened by various methods such as treatment with acid or desilylation with fluoride. Using this reaction sequence, y-lactones 52 with various substituents can be obtained by the intramolecular attack of the ketone oxygen on the siloxy-substituted carbon followed by oxidation with pyridinium chlorochromate. The cyclic hemiacetal intermediates 53 can be converted to the tetrahyd-rofuran derivatives 55 by deoxygenation with triethylsilane/boron trifluoride. 

Cyclopropenylium ions 1 were converted into the corresponding cyclopropenes 2 by the addition of hydride ion derived from various hydride sources, such as lithium aluminum hydride,sodium borohydride, borane-amine complex, triethylsilane, and tributyl-tin hydride. Particularly in the case of borohydride reduction of the diphenylcyclo-propenylium ion, the order of reagent addition was quite important. The slow addition of an acetonitrile solution of the cyclopropenylium salt into a solution of the borohydride gave the cyclopropene derivative,whereas the inverse order of addition resulted in quantitative formation of 1,2,4,5-tetraphenylbenzene (see Section 2.1.2.3.), No such precaution of the inverse addition was required in the case of borane-amine reduction of the l-chloro-2,3-diphenyl-cyclopropenylium ion. ... 

ALDEHYDES 9-Borabicyclo[3.3.1]-nonane. Diazoacetaldehyde. Diethyl-allylthiome thylphosphonate, Diethyl phenyl orthoformate Dithiane. Lith-ium-Alkylamine. Lithium diisopropyl-amide. Sodium tetracarbonylferrate-(TI). 1,1,3,3-Tetramethylbutylisonitrile. 2,4,4,6-Tetramethyl-5,6-dihydro-l, 3-(4H)-oxazine. Triethylsilane. s-Trithiane. 

Vinylsilanes have also been prepared from the same precursors. Thus treatment of (1), R = CHj, with lithium ethoxide (1, 612-613) in benzene containing triethylsilane gives triethyl (2-methyl-l-propenyl)silane (5) in 61% yield. Since carbenes are known to insert into the SiH bond, an unsaturated carbene (4) is apparently involved.2... 

Hydrodesulfnrisation of benzothiophenes is conveniently achieved using Raney nickel. Reduction of the hetero-rings of both benzofuran and benzothiophene giving 2,3-dihydro derivatives, notably with retention of the snlfur in the latter case, can be achieved using triethylsilane in acidic solution, or with hydrogen over colloidal rhodium. Reductive cleavage of benzofuran to 2-hydroxystyrene is caused by lithium with 4,4 -di-f-butylbiphenyl (DTBB). ... 

The hydrosilylation of carbodiimides with organyl-tf-silanes in the presence of a catalyst such as PdCl2 or tris(triphenylphosphine)rhodium(I) chloride can give rise to AT-organylsilylformamidines, e.g., from diisopropylcarbodiimide (443) and triethylsilane (442) in the presence of PdCl2 A N -diisopropyl-N-triethylsilylformamidine (444) is formed (equation 206)226. Also lithium diisopropylamide reacts with N-phenylimines... 

Lithium triethylborohydride. CARBONYL COMPOUNDS Catechol-borane. Triethylsilane-Boron triflaoride. EPOXIDES Iron carbonyl. Methyltri-phenoxyphosphonium iodide. Sodium 0,0-diethyl phosphoiotelluioate. Tti-fluoroacetic anhydride-Sodium iodide. 

Triethylsilane in 3M ethereal Lithium Perchlorate solution effects the reduction of secondary allylic alcohols and acetates (eq 18). The combination of triethylsilane and Titanium(IV) Chloride is a particularly effective reagent pair for the selective reduction of acetals. Treatment of ( )-frontalin with this pair gives an 82% yield of tetrahydropyran products with a cis. trans ratio of 99 1 (eq 19). This exactly complements the 1 99 product ratio of the same products obtained with Diisobutylaluminum Hydride. ... 

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