Zinc-Dimethylformamide

Phosphoryl chloride Carbon disulflde, A,A-dimethylformamide, 2,5-dimethylpyrrole, 2,6-dimethyl-pyridine 1-oxide, dimethylsulfoxide, water, zinc... 

Reductive dunenzation to form fluorinated benzopinacols proceeds m the partly fluormated case either with zinc or by photolysis but is not observed with perfluorobenzophenone [651 (equation 53). Trifluoroacetophenone is reduced electrochemically in dimethylformamide to a stable radical anion, which, m the presence ot lithium ion, rapidly dunerizes to pinacol in higher yield than that available by photoreduction [66] (equation 54)... 

In a similar reaction, iodine fluonde also can be removed from perfluorobutyl-, perfluorohexyl-, and perfluorooctyl iodide by using zinc-copper couple in dimethyl sulfoxide or dimethylformamide [71]... 

A poly(L-lysine) dendrimer 23 which carries 16 free-base porphyrins in one hemisphere and 16 Zn porphyrins in the other has been synthesized and studied in dimethylformamide solution [54]. In such a dendrimer, energy transfer from the Zn porphyrins to the free-base units can occur with 43% efficiency. When the 32 free base and zinc porphyrins were placed in a scrambled fashion, the efficiency of energy transfer was estimated to be 83% [55]. Very efficient (98%) energy transfer from Zn to free-base porphyrins was also observed in a rigid, snowflake-shaped structure in which three Zn porphyrin units alternate with three free-base porphyrin units [56]. 

Calorimetry investigations of zinc ions with functionalized pyridines have been carried out in both dimethylformamide and acetonitrile. The pyridines used were pyridine, 3-methylpyridine, and 4-methylpyridine. In DMF, for all three pyridines, four- and six-coordinate species formed and their formation constants, reaction enthalpies and entropies were determined. The stability increases linearly with increasing basicity of the pyridine derivative. The formation of the 3-methylpyridine complex is enthalpically less favorable and entropically more favorable than... 

Kim and Varma have described the preparation of a range of cyclic ureas from diamines and urea [366]. In the example highlighted in Scheme 6.203, ethylenedi-amine and urea were condensed in the presence of 7.3 mol% of zinc(II) oxide in N,N-dimethylformamide as solvent at 120 °C to furnish imidazolidin-2-one in 95% isolated yield. Key to the success of this method is that the reaction needs to be performed under reduced pressure in order to remove the ammonia formed from the reaction mixture. This method was extended to a variety of diamines and amino alcohols [366]. 

Zinc powder, obtainable from Mallinckrodt Chemical Works, St. Louis, Missouri, and Merck and Co., Rahway, New Jersey, is placed in a beaker and is washed consecutively and rapidly ( 10 seconds) with three 100-ml. portions of 3% hydrochloric acid, two 100-ml. portions of water, two 200-ml. portions of 2% aqueous copper sulfate (until blue color disappears), two 200-ml. portions of water, two 100-ml. portions of acetone, two 100-ml. portions of dimethylformamide, and is washed into the reaction vessel with dimethylformamide. This procedure is a modification of one described by Hennion and Sheehan.3... 

In addition to these physical studies at the Bureau, Tipson was able to return to his synthetic interests, both alone and in collaboration with other staff members. He was especially pleased to prepare D-talose in crystalline form, an accomplishment that had eluded Emil Fischer. Pursuing his longstanding interest in the reaction of sulfonic esters with iodide and following an earlier observation that the tetratosyl ester of erythritol is converted into butadiene by the action of sodium iodide and zinc, he demonstrated (with A. Cohen) that nonterminal unsaturation may be conveniently introduced into alditol derivatives by reaction of contiguous secondary sulfonates with sodium iodide and zinc dust in boiling A.A-dimethylformamide. This Tipson-Cohen reaction subsequently proved of great utility in other hands for the conversion of more complex carbohydrate structures into vicinal dideoxy derivatives. 

Divalent chromium salts show very strong reducing properties. They are prepared by reduction of chromium(III) compounds with zinc [187] or a zinc-copper couple and form dark blue solutions extremely sensitive to air. Most frequently used salts are chromous chloride [7SS], chromous sulfate [189], and less often chromous acetate. Reductions of organic compounds are carried out in homogeneous solutions in aqueous methanol [190], acetone [191], acetic acid [192], dimethylformamide [193] or tetrahydrofuran [194] (Procedure 37, p. 214). 

Reduction of a range of allyl and benzyl chlorides at a stainless steel cathode in dimethylformamide in the presence of carbonyl compounds and using a sacrificial anode of aluminium or zinc, leads to a Reformatsky-type reaction in 40-80 % yields. Allyl halide give products by reaction at both the a- and y-positions. Tetra-chioromethane and bromotrifluoromethane take part in similar reactions provided a... 

A highly active zinc powder can be generated in bulk by electrolysis of a tetraalkylammonium salt in dimethylformamide between a zinc anode and a platinum cathode [183]. This reagent has been used in stoichiometric amounts for Re-formatsky-type reactions where the tribromide 61 is used as a precursor for the isoprenyl group [184]. Zinc promoted 1,4-elimination of bromine to give the butadiene system is followed by a Reformatsky reaction of the remaining allylic bromine substituent. 

The cross coupling of two aryl halides is achieved by the use of organozinc intermediates. Reduction of one component is carried out in dimethylformamide using a stainless steel cathode and a zinc anode with the nickel catalyst in the pres-... 

Since their discovery in 1866, it has been known that sulphoxides are reducible by zinc and acid to the conesponding sulphide [63], fhe equivalent electrochemical process cannot be characterised because sulphoxides also decrease the hydrogen overpotential [64], Dialkyl sulphoxides are not reduced in absence of protons and dimethyl sulphoxide is used as a solvent for electrochemical reduction. Phenyl methyl sulphoxide gives a single two-electron wave on polarography in both ethanol (E./, = -2.17 V vs. see) and dimethylformamide (E./, = -2.32 V vs. see), forming phenyl methyl sulphide [65],... 

Trichloro-l,3,5-triazine, Dimethylformamide 2,4,6 -Tris (bromoamino) -1,3,5 -triazine Zinc, Water... 

Reductive processes are sometimes useful for conversion of polyiodinated pyrroles into compounds with fewer iodine atoms. Sequential action of butyl-lithium and water reduced tetraiodopyrrole to a mixture of 2,3,4-triiodopyrrole (63%) and 2,3,5-triiodopyrrole (3%). Zinc and acetic acid was able to reduce the tetraiodo compound to 3,4-diiodopyrrole which was converted by butyl-lithium and then dimethylformamide into 3-formyl-... 

Most linear ceilulosics may be dissolved in solvents capable of breaking the strong hydrogen bonds. These solvents include aqueous solutions of inorganic acids, zinc chloride, lithium chloride, dimethyl dibenzyl ammonium hydroxide, and cadmium or copper ammonia hydroxide (Schweizer s reagent). Cellulose is also soluble in hydrazine, dimethyl sulfoxide in the presence of formaldehyde, and dimethylformamide in the presence of lithium chloride. The product precipitated by the addition of nonsolvents to these solutions is highly amorphous and is called regenerated cellulose. 

The activated zinc obtained by electrochemical reduction of Zn2+ in dimethylformamide has been used for the isoprenylation of aldehydes and ketones. This has been reported by Tokuda and coworkers (equation 4)10. 

This last electrochemical process is carried out in an undivided electrolysis cell fitted with a sacrificial magnesium anode and a nickel foam as cathode. The reaction is conducted in dimethylformamide in the presence of both NiBr2(bpy) as the catalyst and dried ZnBr2 (1.1 molar equivalents with respect to bromothiophene), which is used both as supporting electrolyte and as a zinc(II) ion source. The other conditions are the same as those described in the section concerning the aromatic halides. The yield of 3-thienylzinc bromide was roughly 80%, as determined by GC analysis after treatment with iodide (equation 34). 

The reduction of l-alkyl-8,8-dibromo-bicyclo[5.1.0]octanes by methyl magne-siumbromide in tetrahydrofuran provides mixtures of fully and partially reduced products [31], A comparable result is obtained when zinc in dimethylformamide... 

Nonacarbonyldiiron in the presence of activated zinc as well as disodium tetracarbonylferrate have both been utilized to dechlorinate dimethyl cispransjransA,2,3,4-tetrachlorocyclobutane-1,2-dicarboxylate (41), which leads to [dimethyl l,2,3,4- 7-l,3-cyclobutadiene-l,2-dicarboxy-latejiron tricarbonyl (42) in 1 and 35-40% yield, respectively.15 As a result of the better leaving tendency of the bromide anion, the yield of 42 can be improved to 70% by reaction of the analogous dibromide with nonacarbonyldiiron in dimethylformamide.16 In another experiment, debromination with activated zinc in tetrahydrofuran converts cyclobutane-1,2-di-carboxylate 43 to cyclobutene-1,2-dicarboxylate 44 in 58% yield.15... 

The following procedure is an operatively simple route for the synthesis of bromotrimethylsilane on a preparative laboratory scale from reagents that are readily accessible and inexpensive. This could be a method of choice in some laboratories despite the fact that bromotrimethylsilane is now commercially available (Petrach Systems, Aldrich, or Alpha). Moreover, the procedure also serves as a suitable method for the synthesis of azidotrimethylsilane and isocyanatotrimethylsilane, and is specially useful for the preparation of cyanotrimethylsilane. Thus a mixture of triphenylphosphine dibromide, hexamethyldisiloxane, and a catalytic amount of powdered metal zinc in 1,2-dichlorobenzene is heated under reflux to produce bromotrimethylsilane in nearly quantitative yield, which is simultaneously distilled over a suspension of the corresponding pseudohalogenoacid salt in N, /V-dimethylformamide as solvent.6... 

Further improvements in dehalogenation selectivity and yields can be achieved by using dipolar aprotic solvents. Dimethylformamide has mostly been used for this purpose,18,56,84 97 although dimethyl sulfoxide,98,99 especially when combined with sonication at room temperature (vide infra), deserves attention in particular cases.100,101 Other polar and dipolar aprotic solvents have also been used, namely, acetone,4 butan-2-one,4 acetonitrile,102 acetic anhydride,103104 ethyl acetate,61 tetrahydrothiophene 1,1-dioxide (sulfolane)105 and hexamethyl-phosphoric triamide,106 but no details were reported on their advantages over dimelhylform-amide or dimethyl sulfoxide. Better performance of dipolar aprotic solvents, such as dimethyl-formamide, over other solvents has been demonstrated in the recent comparison of the dehalogenation of 4,5-dichloro-4,5,5-trifluoropentan-l-ol (4) with zinc in various solvents.90... 

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