Dimethylformamide with 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)... 

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). 

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... 

Recently, the formation of stable perfluoroalkenylzinc compounds RCF = C(ZnBr)R by elimination of BrF with zinc in dimethylformamide from fluorohalo compounds RCF2CBr2R has been reported177"179 (see Vol. ElOb/ Part 1, pp472, 473). Some of these compounds can be thermally decomposed to fluoroalkenes RCF = CHR, e.g. formation of 2.179... 

First, 1,1,1-trichlorotrifluoroethane reacts with zinc to form an organometallic complex with dimethylformamide (DMF) ... 

Reduction of a,a -dibromo ketones. Reduction of 2,4-dibromo-2,4-dimethyl-pentane-3-one (1) with ultrasonically dispersed mercury in the presence of a ketone such as acetone leads to a 4-methylene-l,3-dioxolane (2) in about 50% yield. A similar reaction has been observed in the reduction of dibromo ketones with zinc in dimethylformamide (5, 221). 2-Oxyallyl cations such as a have been invoked as intermediates in reductions of dihalo ketones with various metals. 

Tetrafluoropyridyl organometallic reagents can be prepared by reaction of 4-bromotetra-fluoro- or tctrafluoro-4-iodopyridine with zinc or cadmium in dimethylformamide at room temperature.83 Metathesis of these reagents with copper(l) bromide affords the (2.3,5,6-tetra-fluoro-4-pyridyl)copper reagent. The latter species undergoes high-yield substitution reactions with allyl halides, vinyl iodides, aryl iodides, and alkanoyl halides. 

Monofluoroalkenes have been prepared by the addition of fluoromethylene-triphenylphosphorane generated m situ by treatment of fluoroiodomethyltri-phenylphosphonium iodide with zinc-copper couple in dimethylformamide [49] (equabon 47) (Table 18>. 

Under rather complex conditions, bromobenzene is reduced to benzene by heating with zinc powder and nickel chloride in dimethylformamide or hexamethylphosphoramide containing small amounts of water (Table 4). ... 

Reaction of 2,2,4,4-tetrachlorobutanes with zinc in dimethylformamide gave 1,2-dialkyl-cyclopropenes in good yields.- ... 

The dechlorination of 2,3,5,6-tetrachloro-2,3-difluoro-2,3-dihydro-l,4-dioxin with zinc in dimethylformamide afforded 2,3-dichloro-5,6-difluoro-1,4-dioxin as a distillate contamination with dimethylformamide <91J0C3915>. In the oxathiin series, sulfur dichloride added to vinylic ethers gave 2,6-dichloro-l,4-oxathianes (197). Dehydrohalogenation of these products by potassium t-butoxide gives the fully unsaturated compounds 1,4-oxathiin and 3,5-dimethyl-l,4-oxathiin (198) in moderate to reasonable yields <80RTC12>. 

Introduction of multidentate co-ligands to bio-MOFs significantly increases their structural diversity. When 4,4 -biphenyldicarboxylic acid is combined with zinc acetate and adenine in dimethylformamide (DMF), solvothermal synthesis yields bio-MOF-1, which is formulated as [Zn8(ad)4(BPDC)gO] -2[Me2NH2] ... 

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... 

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. 

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-... 

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