Dehydrohalogenation of ethyl halides

Unimolecular decomposition kinetics of selected ethyl halides, phenethyl halides and methoxyphenethyl halides have been investigated using high level computational chemistry methods. The phenethyl halides decompose faster than the ethyl halides due to a more electronegative chlorine atom, induced by the chloroethyl functionality as an electron-withdrawing group. 1-Chloro-2-(methylthio)ethane exhibits faster dehydrochlorination than that of chloroethane/1-chloro-2-methoxyethane, owing to more polarisable C?H and C?Cl bonds in the transition structures. Calculations suggest that electronic factors rather than anchimeric assistance influence the dehydrochlorination reactions.     

A one-pot, three-component synthesis of thiazolidine-2-thiones

An efficient method for the synthesis of thiazolidine-2-thiones is described via regiospecific iodocyclization of an allyl amine, carbon disulfide, and iodine. Dehydrohalogenation of the iodo-derivatives gives thiazole-2(3H)-thiones. In addition, nucleophilic substitution of the iodine in the products is accomplished using NaN₃, thiophenol, or dithiocarbamate.     

去卤缩聚法合成蓝色电致发光聚合物聚（2,5—二庚基）对苯乙炔

利用双卤甲基苯衍生物在强碱诱导下的缩合反应，合成了共轭态可溶的聚对苯乙炔，并利用ＩＲ，ＵＶ－Ｖｉｓ，＾１Ｈ－ＮＭＲ，ＴＧＡ等对聚合物结构与性能进行了有征，其Ｎｎ＝０．４８×１０＾４。电致发光器件的发光峰值波长为４８６ｎｍ，起亮电压为２２Ｖ。     

Isoxazoles from 1,1-Disubstituted Bromoalkenes

The regioselective synthesis of 3,5-disubstituted isoxazoles was achieved through the 1,3-dipolar cycloaddition of nitrile oxides with 1,1-disubstituted bromoalkenes. The substituted bromoalkenes function as alkyne synthons which were used to construct 5,5-disubstituted bromoisoxazoline intermediates that aromatize to the analogous isoxazoles through the loss of HBr.     

Synthetic utility of 3-(perfluoro-1,1-dimethylbutyl)prop-1-ene. Part VI. A free-radical addition of CCl4 and CBr4 and dehydrohalogenation of the adducts

Heating the title compound 1 in excess CCl₄ and in the presence of a free-radical initiator (t-butyl peroxide) at 120 °C afforded 1,1,1,3-tetrachloro-4-(perfluoro-1,1-dimethylbutyl)butane (2) as the main product together with considerable amounts of cyclic dimer, 1,4-bis(perfluoro-1,1-dimethylbutyl)cyclohexane (3). Reaction of 1 with CBr₄ at 120 °C gave 1,1,1,3-tetrabromo-4-(perfluoro-1,1-dimethylbutyl)butane (4) as the sole product while at 220 °C a mixture of 1,2-dibromo-3-(perfluoro-1,1-dimethylbutyl)propane (5) and 1,1-dibromo-4-(perfluoro-1,1-dimethylbutyl)buta-1,3-diene (6) was formed. Treatment of adducts 2 and 4 with methanolic potassium hydroxide at ambient temperature gave mixtures of 1,1,3-trihalo-4-(perfluoro-1,1-dimethylbutyl)but-1-enes (7) or (8) and 1,1-dihalo-4-(perfluoro-1,1-dimethylbutyl)buta-1,3-dienes (9) or (6) in ratios depending on the adduct to base ratio and on the reaction conditions. Using an excess of the base and reflux temperature, adduct 4 and diene 6 were converted into methyl 4-(perfluoro-1,1-dimethylbutyl)buten-3-oate (10).     

Terminal alkynes from aldehydes via dehydrohalogenation of (Z)-1-iodo-1-alkenes with TBAF

Terminal alkynes were prepared in near quantitative yields via dehydrohalogenation of (Z)-1-iodo-1-alkenes with tetrabutylammonium fluoride (TBAF) under mild conditions. The methodology was expanded to include a one-pot, direct synthesis of terminal alkynes from aldehydes without the necessity of isolating and purifying the intermediate iodoalkene.     

Regioselective synthesis of O- and O-cyclopyrimidine nucleoside analogues

Regioselective synthesis of two new series of cyclonucleoside analogues from the 1,2-carbonucleoside of uracil 1a: O²,7′-cyclonucleosides (3a-c) and O⁶,7′-cyclonucleosides (4a-c), analogues of pyrimidine (cyclohexane derivatives) is reported. Synthesis of O²-cyclonucleoside analogues was performed by activation of the hydroxymethyl group of carbocyclic moiety and using the carbonyl group at position 2 of the heterocyclic base as a nucleophile. Synthesis of O⁶-cyclonucleoside analogues was achieved by nucleophilic attack of the 7′-hydroxyl group on the electron-deficient 6-position and subsequently dehydrohalogenation in basic conditions.     

One- versus two-electron reaction pathways in the electrocatalytic reduction of benzyl bromide at silver cathodes

The electrocatalytic reduction of benzyl bromide at a silver cathode has been investigated in acetonitrile in the absence and presence of acids, using cyclic voltammetry (CV) and controlled-potential electrolysis (CPE). CV gives rise to two reduction waves, which represent the dissociative 1e⁻ reduction of PhCH₂Br to and Br⁻ followed by a further reduction of the benzyl radical to at more negative potentials. The charge stoichiometry (1e⁻ vs 2e⁻/molecule) and product distribution depend on the applied potential and reaction medium. In the absence of added acids, the reduction of PhCH₂Br at potentials of the first wave is a 1e⁻ process mainly yielding bibenzyl, whereas toluene becomes the principal product at potentials beyond the second wave. The addition of acids strongly modifies the dependence of selectivity on the applied potential. The presence of a strong acid changes the mechanism of the process, which now becomes a 2e⁻ reduction to toluene, even at potentials corresponding to the first reduction wave.     

Microwave‐Assisted Elimination Reaction of trans‐4‐(4‐Fluorophenyl)‐3‐chloromethyl‐1‐methylpiperidine on Alumina

Abstract

trans‐4‐(4‐Fluorophenyl)‐3‐chloromethyl‐1‐methylpiperidine 3b was subjected to elimination reaction on alumina or KF‐alumina under solvent‐free conditions and microwave irradiation. Compared with the “classical” method of heating in the presence of an organic base, the microwave‐assisted methodology provided higher yields of 4‐(4‐fluorophenyl)‐3‐methylene‐1‐methylpiperidine 7b (65.5–71%) in considerably shorter reaction times (20–40 min). Furthermore, the exocyclic double bond in 7b underwent rearrangement to the endocyclic double bond to furnish compound 8. The effect of alumina and irradiation time on reaction conversion and the extent of isomerization was examined.