Tetrahydrofuran metal

These are commonly prepared by treatment of the corresponding neutral molecule with an alkali metal dissolved or finely dispersed in an inert solvent such as tetrahydrofuran. Metal-ammonia solutions are generally less satisfactory because protonation and then further reduction may follow initial formation of the required anion. 

When a mixture of a cyclopropyl phenyl selenone and a ketone or an aldehyde is treated with potassium tert-butoxide in tetrahydrofuran, metalation of the selenone takes place preferentially and the metalloselenone formed immediately reacts with the carbonyl compound. Oxaspiropentanes are produced almost quantitatively when ketones are used whereas a mixture of oxaspiropentanes and cyclopropyl ketones are obtained when the reaction is carried out with aldehydes, for example, formation of 5 and... 

Catalytic hydrogenation of furan to tetrahydrofuran is accompHshed in either Hquid or vapor phase. Hydrogenation of the double bonds is essentially quantitative over nickel catalysts but is generally accompanied by hydrogenolysis over the noble metals. 

There are five components to the cost of using a Grignard reagent (/) magnesium metal, (2) the haUde, (J) the solvent, (4) the substrate, and (5) disposal of the by-products. The price of magnesium in mid-1992 was 3.20/kg, having risen from 1.20/kg in 1966 to 1.36/kg in 1970 and 2.90/kg in 1979. Prices for tetrahydrofuran and diethyl ether, the two most commonly used solvents, have also increased (Table 3) in the same period. The cost of the hahde depends on its stmcture, but as a general rule the order of cost is chloride < bromide < iodide. 

These reactions are usehil for the preparation of homogeneous difunctional initiators from a-methylstyrene in polar solvents such as tetrahydrofuran. Because of the low ceiling temperature of a-methylstyrene (T = 61° C) (26), dimers or tetramers can be formed depending on the alkaU metal system, temperature, and concentration. Thus the reduction of a-methylstyrene by sodium potassium alloy produces the dimeric dianionic initiators in THF (27), while the reduction with sodium metal forms the tetrameric dianions as the main products (28). The stmctures of the dimer and tetramer correspond to initial tail-to-tail addition to form the most stable dianion as shown in equations 6 and 7 (28). 

GopolymeriZation Initiators. The copolymerization of styrene and dienes in hydrocarbon solution with alkyUithium initiators produces a tapered block copolymer stmcture because of the large differences in monomer reactivity ratios for styrene (r < 0.1) and dienes (r > 10) (1,33,34). In order to obtain random copolymers of styrene and dienes, it is necessary to either add small amounts of a Lewis base such as tetrahydrofuran or an alkaU metal alkoxide (MtOR, where Mt = Na, K, Rb, or Cs). In contrast to Lewis bases which promote formation of undesirable vinyl microstmcture in diene polymerizations (57), the addition of small amounts of an alkaU metal alkoxide such as potassium amyloxide ([ROK]/[Li] = 0.08) is sufficient to promote random copolymerization of styrene and diene without producing significant increases in the amount of vinyl microstmcture (58,59). 

Other, even milder bases than LDA and LHS, such as lithium methoxide and lithium /-butoxide, may be used in organic syntheses (143,144). Lithium methoxide is available commercially as a 10% solution in methanol and lithium /-butoxide as an 18% solution in tetrahydrofuran (145). Lithium /-butoxide is also soluble in hydrocarbon solvents (146). Both lithium alkoxides are also available as soHds (147) (see Alkoxides, metal). 

Alkylation and arylation of organosilanes occur readily with alkyl and aryl alkaU metal compounds. Yields from these reactions are good but are iafluenced by steric requirements on both silane and metal compounds. There is Httie iaductive effect by the organic groups attached to siUcon, as measured by the yield of products (126,127). These reactions proceed more readily ia tetrahydrofuran and ethyl ether than ia ligroin or petroleum ether, where R and are alkyl or aryl and M is Li, Na, or K. 

Lithium metal in tetrahydrofuran can also be used as the coupling reagent, and unsymmetrical ditins can be prepared when the reaction is conducted in stages (162,163). 

Sodium borohydride is manufactured by Morton International, Inc. Treatment of trimethyl borate with a metal hydride, eg, NaH, ia the absence of a solvent yields sodium hydrotrimethoxyborate [16940-17-3] Na[HB(OCH2)3], (eq. 50) which disproportionates ia the presence of solvents such as tetrahydrofuran at 60—70°C (eq. 51) (112). 

It resembles tetracyanoethylene in that it adds reagents such as hydrogen (31), sulfurous acid (31), and tetrahydrofuran (32) to the ends of the conjugated system of carbon atoms suffers displacement of one or two cyano groups by nucleophilic reagents such as amines (33) or sodiomalononittile (34) forms TT-complexes with aromatic compounds (35) and takes an electron from iodide ion, copper, or tertiary amines to form an anion radical (35,36). The anion radical has been isolated as salts of the formula (TCNQ) where is a metal or ammonium cation, and n = 1, 1.5, or 2. Some of these salts have... 

Alkali Metal Catalysts. The polymerization of isoprene with sodium metal was reported in 1911 (49,50). In hydrocarbon solvent or bulk, the polymerization of isoprene with alkaU metals occurs heterogeneously, whereas in highly polar solvents the polymerization is homogeneous (51—53). Of the alkah metals, only lithium in bulk or hydrocarbon solvent gives over 90% cis-1,4 microstmcture. Sodium or potassium metals in / -heptane give no cis-1,4 microstmcture, and 48—58 mol % /ram-1,4, 35—42% 3,4, and 7—10% 1,2 microstmcture (46). Alkali metals in benzene or tetrahydrofuran with crown ethers form solutions that readily polymerize isoprene however, the 1,4 content of the polyisoprene is low (54). For example, the polyisoprene formed with sodium metal and dicyclohexyl-18-crown-6 (crown ether) in benzene at 10°C contains 32% 1,4-, 44% 3,4-, and 24% 1,2-isoprene units (54). 

Dianion formation from 2-methyl-2-propen-l-ol seems to be highly dependent on reaction conditions. Silylation of the dianion generated using a previously reported method was unsuccessful in our hands. The procedure described here for the metalation of the allylic alcohol is a modification of the one reported for formation of the dianion of 3-methyl-3-buten-l-ol The critical variant appears to be the polarity of the reaction medium. In solvents such as ether and hexane, substantial amounts (15-50%) of the vinyl-silane 3 are observed. Very poor yields of the desired product were obtained in dirnethoxyethane and hexamethylphosphoric triamide, presumably because of the decomposition of these solvents under these conditions. Empirically, the optimal solvent seems to be a mixture of ether and tetrahydrofuran in a ratio (v/v) varying from 1.4 to 2.2 in this case 3 becomes a very minor component. 

The reaction mixture contained 0.33 g-atom of metal, 200 ml of liquid ammonia, 0.85 mole of alcohol and 80 ml of tetrahydrofuran. 

Aromatic steroids are virtually insoluble in liquid ammonia and a cosolvent must be added to solubilize them or reduction will not occur. Ether, ethylene glycol dimethyl ether, dioxane and tetrahydrofuran have been used and, of these, tetrahydrofuran is the preferred solvent. Although dioxane is often a better solvent for steroids at room temperature, it freezes at 12° and its solvent effectiveness in ammonia is diminished. Tetrahydrofuran is infinitely miscible with liquid ammonia, but the addition of lithium to a 1 1 mixture causes the separation of two liquid phases, one blue and one colorless, together with the separation of a lithium-ammonia bronze phase. Thus tetrahydrofuran and lithium depress the solubilities of each other in ammonia. A tetrahydrofuran-ammonia mixture containing much over 50 % of tetrahydrofuran does not become blue when lithium is added. In general, a 1 1 ratio of ammonia to organic solvents represents a reasonable compromise between maximum solubility of steroid and dissolution of the metal with ionization. 

Toluene is a useful co-solvent in metal-ammonia reductions as first reported by Chapman and his colleagues. The author has found that a toluene-tetrahydrofuran-ammonia mixture (1 1 2) is a particularly useful medium for various metal-ammonia reductions. Procedure 8a (section V) describes the reduction of 17-ethyl-19-nortestosterone in such a system. Ethylene dibromide is used to quench excess lithium. Trituration of the total crude reduction product with methanol affords an 85% yield of 4,5a-dihydro-17-ethyl-19-nortestosterone, mp 207-213° (after sintering at 198°), reported mp 212-213°. For the same reduction using Procedure 5 (section V), Bowers et al obtained a 60% yield of crude product, mp, 196-199°, after column chromatography of the total reduction product. A similar reduction of 17-ethynyl-19-nortestosterone is described in Procedure 8b (section V). The steroid concentration in the toluene-tetrahydrofuran-ammonia system is 0.05 M whereas in the ether-dioxane-ammonia system it is 0.029 M. 

The general reaction procedure and apparatus used are exactly as described in Procedure 2. Ammonia (465 ml) is distilled into a 2-liter reaction flask and to this is added 165mlofisopropylalcoholandasolutionof30g(0.195 mole) of 17/ -estradiol 3-methyl ether (mp 118.5-120°) in 180 ml of tetrahydrofuran. The steroid is only partially soluble in the mixture. A 5 g portion of sodium (26 g, 1.13 g-atoms total) is added to the stirred mixture and the solid dissolves in the light blue solution within several min. As additional metal is added, the mixture becomes dark blue and a solid (matted needles) separates. Stirring is inefficient for a few minutes until the mass of crystals breaks down. All of the sodium is consumed after 1 hr and 120 ml of methanol is then added to the mixture with care. The product is isolated as in Procedure 4h 2. After being air-dried, the solid weighs 32.5 g (ca. 100% for a monohydrate). A sample of the material is dried for analysis and analyzed as described in Procedure 2 enol ether, 91% unreduced aromatics, 0.3%. The crude product may be crystallized from acetone-water or preferably from hexane. 

Alkali-metal graphites are extremely reactive in air and may explode with water. In general, reactivity decreases with ease of ionization of M in the sequence Li > Na > K > Rb > Cs. Under controlled conditions H2O or ROH produce only H2, MOH and graphite, unlike the alkali-metal carbides M2C2 (p. 297) which produce hydrocarbons such as acetylene. In an important new reaction CgK has been found to react smoothly with transition metal salts in tetrahydrofuran at room temperature to give the corresponding transition metal lamellar compounds ... 

Sebastian also observed that although alkylation of the indole Grignard reagent with methyl iodide in tetrahydrofuran at 23° gave essentially 3-methylindolc, variable amounts of 1- and 3-methyl-indole were obtained on alkylation of the alkali metal salts of indole under similar conditions. Sebastian s results were qualitatively similar to those obtained earlier by Lerner and more recently by Cardillo who studied the reaction of a number of organometalhc... 

By reaction of an a-halo ester 1 with zinc metal in an inert solvent such as diethyl ether, tetrahydrofuran or dioxane, an organozinc compound 2 is formed (a Grignard reagent-like species). Some of these organozinc compounds are quite stable even a structure elucidation by x-ray analysis is possible in certain cases ... 

A solution of 1.5 g of dl-3-(1, r-dimethylheptyi)-6,6a,7,8-tetrahydro-1-hydroxy-6,6-di-methyl-9H-dibenzo(b,d] pyran-9-one in 50 mi of anhydrous tetrahydrofuran (THF) was added dropwise to a soiution of iithium metal in liquid ammonia at -80°C. Excess iithium metal was added in chunks to the solution as the biue color, indicating free dissolved lithium, disappeared. After the addition was complete, ammonium chloride was added to react with any excess lithium metal still present. 

Hydrogenation of diethylmaleate in the vapor phase over a nonprecious metal catalyst produces diethyl succinate. Successive hydrogenation produces y-butyrolactone, butanediol, and tetrahydrofuran. 

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