2-Butyne, 1,4-dibromo

Acetylene is condensed with carbonyl compounds to give a wide variety of products, some of which are the substrates for the preparation of families of derivatives. The most commercially significant reaction is the condensation of acetylene with formaldehyde. The reaction does not proceed well with base catalysis which works well with other carbonyl compounds and it was discovered by Reppe (33) that acetylene under pressure (304 kPa (3 atm), or above) reacts smoothly with formaldehyde at 100°C in the presence of a copper acetyUde complex catalyst. The reaction can be controlled to give either propargyl alcohol or butynediol (see Acetylene-DERIVED chemicals). 2-Butyne-l,4-diol, its hydroxyethyl ethers, and propargyl alcohol are used as corrosion inhibitors. 2,3-Dibromo-2-butene-l,4-diol is used as a flame retardant in polyurethane and other polymer systems (see Bromine compounds Elame retardants). 

Indium can effectively mediate the coupling of l,4-dibromo-2-butyne with aldehydes in a 1 1 ratio to give l,3-butadien-2-yl-methanols in aqueous media (Eq. 8.83).211 When a 1 2 ratio was used, the reaction... 

Methyl iodide (31) reacts with silver nitroform (32) in acetonitrile to give a 51 % yield of 1,1,1-trinitroethane (33). ° The potassium salt of nitroform in acetone has been used for the same reaction.Yields between 28 % and 65 % have been reported for the reaction of silver nitroform in acetonitrile with higher molecular weight alkyl iodides. The choice of solvent is important in some reactions, for example, silver nitroform reacts with l,4-dibromo-2-butyne (34) in solvents like dioxane and acetone to give l,l,l,6,6,6-hexanitro-3-hexyne (35) in approximately 72 % yield, whereas the same reaction in acetonitrile is reported to give a mixture of compounds. 

Methyl-l-butene l,2-Dibromo-3-methylbutane 3-Methyl-l-butyne... 

In 2002, the asymmetric synthesis of 3-substituted 3-hydroxy-p-lactams has been reported to be realized by metal-mediated l,3-butadien-2-ylation reactions between 1,4-dibromo-2-butyne and optically pure azetidine-2,3-diones [64]. This latter starting material was prepared via Staudinger reaction followed by sequential transesterification and Swem oxidation (Scheme 15), [65]. 

Indium-promoted reaction of l,4-dibromo-2-butyne with carbonyl compounds gives 1,3-butadiene derivatives via the allenic indium intermediates (Scheme 56).220 Similar indium-mediated l,3-butadien-2-ylation reactions of optically pure azetidine-2,3-diones have been investigated in aqueous media, offering a convenient asymmetric entry to the 3-substituted 3-hydroxy-/ -lactam moiety (Equation (40)). The diastereoselectivity of the addition reaction is controlled by the bulky chiral auxiliary at Q4 221 222... 

A stable diindium compound, 2,3-butadienyldiindium tetrabromide 67, is prepared by the reaction of 1,4-dibromo-2-butyne and indium. The reaction between 67 and different carbonyl compounds in the presence of zinc fluoride gives acetyenic diol almost exclusively as a single diastereomer (Scheme 57).223... 

Ozonolysis of truns-2,3 -Dibromo-2-butene in Inert Solvents. Starting Material. The title compound 23 was prepared by adding bromine to 2-butyne at ca. —30° to —40°C. The reaction produced 23 in more than 95% yield, along with less than 5% of the cis-isomer, 24, and trace amounts of as yet unidentified by-products. 

Zirconacyclopentadienes 23 (R = R = R = R = Et, Pr", Bu", M = Zr, Cp =Cp) react with l,4-dibromo-2-butyne in the presence of CuCl via a tandem inter-intra-molecular cyclization to yield 2,3,4,5-tetrasubstituted styrenes (Equation 11) <2002T1107>. 3-Chloro-(2-chloromethyl)propene reacts with the same set of zirconacyclopentadienes in the presence of CuCl to yield tetrasubstituted methylene cycloheptadienes. Reaction with 3,4-dichlorobutene under identical conditions yields vinylcyclohexadienes. In both cases, tandem inter-intra-molecular allylation occurs. 

Prepd from l,4-dibromo-2-butyne and Ag-nitroform. It has about the same explosive sensitivity and power as PETN. Its hot bar ignition temp is 205°... 

The products obtained by the interaction of tetraphenylbutatriene with Fe(CO)6 (433) or of 1,4-dibromo- or substituted l,4-dibromo-2-butyne with Fe3(CO)i2 in the presence of zinc powder (427, 434) were reported by Nakamura and co-workers to be (RR C=C=C=CRR )-Fe2(CO)5 (R = R = H R=H, R = CH3 R = R = CH3 R = R = CgHs). Joshi (319) subsequently showed, however, that the correct formulation of the product is (RR C=C=C=CRR )Fe2(CO)6. This has been confirmed by both mass spectrometric (346, 436) and crystal structure analyses (319, footnote 13). The preliminary structural analysis reveals a nonlinear carbon skeleton with each iron atom attached to the hydrocarbon by both a a and a n bond (78). 

Problem 8.2 (a) Write the equation for the two-stage addition of bromine to 2-butyne. (b) How will the first two bromine atoms affect the reactivity of the double bond (c) How will this influence the competition for halogen between 2-butyne and 2,3-dibromo-2-butene (d) In what proportions would you mix the reajgents to help limit reaction to the first stage (e) Would you bubble 2-butyne into a solution of Br2 in CCI4, or drip the bromine solution into a solution of 2-butyne ... 

Addition and substitution. Addition of allylindium reagents to allenyl carbinols affords linear products. A net l,3-butadien-2-ylation at the (3-carbon of p-acetoxy-p-lactams results when they are treated with indium and l,4-dibromo-2-butyne. ... 

CaCl2 or LiCl in acetone968 or LiBr in acetone can also be used to replace the tosyloxy group by Cl or Br. Anhydrous CaBr2 (prepared from CaC03 + 2HBr and dried finally at 600° for 2 h) is soluble in absolute ethanol and converts 2-butynylene bis-(p-toluenesulfonate) therein into l,4-dibromo-2-butyne in 90% yield.969... 

The organoindium reagent derived from 5-bromo-l,3-pentadiene reacts at the central carbon atom, whereas 1,4-dibromo-2-butyne behaves as a l,3-butadien-2-ylating agent in the presence of indium in aqueous media. ... 

The high reactivity of propargylic halides toward nucleophiles allows the preparation of some rather strained cyclic alkynes and especially dialkynes, in surprisingly simple ways. Thus, the ten-membered ring 22 can be prepared in one step from methylamine and 1,4-dibromo-2-butyne (20), [12] (Scheme 8-2). 

A series of A,A -disubstituted diazacyclodecadiynes (35) was synthesized by a one-pot reaction between the amine component (R = CH3, C2H5, C 3H7, cyclohexyl) and l,4-dibromo-2-butyne in the presence of K2CO3 in THE giving low (5%) yields (Equation (8)) <91TL2887>. 

Draw structures for these compounds (a) cyclopentane, (b) di-2-butene, (c) 2-hexanol, (d) 1,4-dibromo-benzene, (e) 2-butyne. 

Indium-mediated allylation of a-chlorocarbonyl compounds with various allyl bromides in aqueous media gave the corresponding homoallylic chlorohydrins, which could be transformed into the corresponding epoxides in the presence of a base (Eq. 4.24). ° The reaction of cyclopentadienylindium(I) with aldehydes gives isomeric mixtures in aqueous rnedia. Indium-promoted reaction of l,4-dibromo-2-butyne with carbonyl compounds gave 1,3-butadien-2-ylmethanols via the allenic intermediates. ... 

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