Diacetylenes reduction

The title compounds LTB4, 21 (Z) and 22 (Z), have been synthesized23 by stereoselective reduction with deuterium gas of a 1 1 mixture of the suitable diacetylenic precursors 23 and 24 using Lindlar catalyst or palladium on barium sulphate catalyst (equation 10). Leukotriene B4, a 5-lipoxygenase metabolite of arachidonic acid, playing... 

The realization that tubules may be formed on temperature reduction of polymerized SUVs, prepared from polymerizable diacetylenic phosphatidylcholines (21 where n = 7-16 and m = 5-11), represented a major breakthrough in obtaining the desired supramolecular structure [355-360]. In the initial experiments, 0.4- to 1.0-pm-diameter and 10- to 1000-pm-long tubules were prepared by the gradual lowering of the temperature (to about 38 °Q of 21 (m = 8, n = 9) SUVs [358]. The walk of the tubules had thickness of 10-40 nm and were coated by spiral ripples and helical bilayer strips. Many tubules contained trapped SUVs. Polymerization of the acetylenic moieties greatly enhanced the mechanical and thermal stabilities of the tubules [355-360]. 

Since cholesterol is an important component of many biological membranes mixtures of polymerizable lipids with this sterol are of great interest. In mixed monolayers of natural lipids with cholesterol a pronounced condensation effect , i.e. a reduction of the mean area per molecule of phospholipid is observed68. This influence of cholesterol on diacetylenic lecithin (18, n = 12), however, is not very significant (Fig. 32). Photopolymerization indicates phase separation in this system. Apparently due to the large hydrophobic interactions between the long hydrocarbon chains of... 

Oxidative addition of the copper(I) acetylide to the alkynyl halide with formation of a copper(III) intermediate (15), giving the corresponding diacetylene by reductive elimination [11a]. 

Diolefins have been prepared from diacetylenes and olefinic acetylenes for example, reduction of 2,7-nonadiyne by sodium and liquid ammonia gives trows, [Pg.28]

Darzens condensation, 255 Diacetylenes, partial reduction, 46 preparation, 80, 81 preparations listed in table 5, 84 1,2-Diacyloxy compounds, preparation, 484... 

The energy diagram presented in Fig. 17 is of relevance for the chain initiation process as well. It demonstrates that the 1 eV barrier for chain initiation is determined by the activation energy of the reaction rather than the energy difference between dimer and monomer. Since the reaction requires reduction of the reaction distance from 3.6 A to 2 A, both reacting monomers have to execute torsional motions. Otherwise the diacetylene moiety of one monomer had to be rotated by about 45° into a position parallel to the crystallographic b-axis. This is incompatible with steric constraints... 

Corey and Wat17 found that the method of forming cycloolefins from allylic dihalides and nickel carbonyl provides an unusually efficient route for the formation of large rings. Because it leads to cyclic 1,5-dienes, it makes available a variety of cyclic structures not obtainable in a practical way via the acyloin synthesis. Diacetylenic diols (10) were converted by selective reduction into the corresponding cis.cis- and owu,/ra -ethylenic diols followed by reaction with PBr3 to form the diallylic dibromides (12), which were then cyclized with nickel carbonyl. 

The chemistry of cumulenes has been elucidated largely by R. Kuhn.164 For synthesis of cumulenes, a diacetylene is converted into its di-Grignard reagent, which on treatment with a ketone (fluorenone, benzophenone, di-p-tolyl-ketone, etc.) affords a diacetylenic glycol, whence reduction by chro-mium(II) chloride and hydrochloric acid gives the cumulene(III) ... 

Irradiation of phenyl substituted diacetylenes yields both protonated products and reduction products. The photoreduction products seem to originate from the triplet excited state, since oxygen quenches the photoreduction almost completely. However, oxygen does not quench the polar addition reaction, supporting a singlet excited state mechanism for the formation of type B photoproducts (Cl protonation product). 

The stability, color, and extent of polymerization are influenced by distance of the head group to the diacetylene moiety. When they are in close proximity, better packing of amphiphiles leads to increased degree of polymerization and enhanced stability. If the distance between the head group and the diacetylene is increased it will cause a reduction in the extent of polymerization and increase the probability that the polymer will be colored yellow. ... 

C-Labelled dotriacontane has been used to study the retention of tobacco smoke in the respiratory system of smoke-exposed laboratory animals. High-resolution autoradiography studies within the respiratory tract needed tritium-labelled dotriacontane (34) with a specific activity of 0.5 Cimmol" This compound has been prepared by synthesizing the diacetylene 35 and by its reduction to dotriacontane-15,15,16,16,17,17,18,18- H, 34 (equation 48). Sodium acetylide with myristyl bromide yielded hexadec-l-yne 36. Oxidative coupling of 36 using cupric acetate gave the diyne 35 which, upon reduction with tritium gas in the presence of Adams catalyst, yielded 34, with the specific activity of 0.50 Ci mmol as required. 

The linear polymers were readily formed by both methods. A salient feature in both of the syntheses was the in situ production of a desired carboranylenesiloxane oligomer by the reaction of a lithiated carborane and a chlorinated siloxane species rather than the use of the commercial Dexsil monomer as in the case of Henderson et al. [25] and Houser et al. [29], This has afforded an enormous degree of variation in the compositions of diacetylene-containing carboranylenesiloxane polymers that is not available by the conventional route of Henderson et al. [25]. The effect of the reduction in the diacetylene concentration was apparent in the positions and the intensities of the DSC peak maxima of the crossUnking endotherms of 5a-c. Thus, it was observed that as the concentration of the diacetylene units in the polymer... 

Reduction-triggered pericyclic reaction has been used for the biomimetic total synthesis of endiandric acids A-G [72]. Endiandric acids are polycychc natural products isolated from the Australian plant Endiandra introrsa and exist naturally as a racemic mixture which is found to have very high antibacterial effect [73]. In 1980, Black and coworkers [74] proposed a hypothesis that these polycyclic systems are formed in nature by a series of electrocycUzation reactions. On the basis of this hypothesis, Nicolaou et al. [72c] in 1982 reported an excellent domino reduction/electrocyclization process for the synthesis of endiandric acid A 127 (Scheme 9.25). Selective hydrogenation using a Lindlar catalyst of diacetylenic diol 123 afforded the bicyclic diol 126. The reaction presumably proceeds via polyene 124, which then undergoes a spontaneous 8 [i-electrocyclization to give 125. It follows a second 6n-electrocyclization to afford bicyclic 126, which is further converted to endiandric acid A 127. 

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