Dienes partial reduction

The checkers observed only partial reduction of the triene and intermediate diene under these conditions, apparently because sufficient water was present in the reaction mixture to prevent adequate partitioning of the olefins between the hydrocarbon layer and the aqueous ethanolic layer containing the diimide. The checkers avoided this difficulty by use of hydrazine containing less than 5% water (95-f- % hydrazine) available from Olin Mathieson Chemical Company or from Eastman Organic Chemicals. This difficulty could probably also be avoided by use of absolute ethanol rather than 95% ethanol. 

RCM of dienes to cycloalkenes provides a useful method for the syntheses of carbo- and heterocycles and thus has been proved to be extremely effective in total synthesis of various natural products. Usually, however, mixtures of (E)- and (Z)-olefms result. In contrast, ring-closing alkyne metathesis provides a reliable route for synthesis of both (E)- and (Z)-macrocycloalkenes in a stereoslective manner taking advantage of stereoselective partial reduction of resulting cycloalkynes. A Lindlar reduction gives (Z)-cycloalkenes, whereas a hydroboration/ protonation sequence afford ( )-cycloalkenes (Equation (23)). Recently, Trost reported an alternative procedure for the synthesis of (E)-olefins from alkynes through hydrosilylation by a ruthenium catalyst. This procedure converts cycloalkyne 130, for example, to vinylsilane 131 and then to (E)-cycloalkene 132 in a stereoselective manner (Scheme 46)7 ... 

Route III More recently a neat alternative synthesis of camphoric acid has been described by Alder (62). l l 2-Trimethylcyclopentadiene [l] and diethyl-acetylene die arboxylate [2] undergo a diene addition reaction to give the diester [3]- Partial reduction yields [U], which is oxidised to the bis-glyoxalate [5] by nitric acid. The latter on decarbonylation yields diethyl camphorate [6] which on hydrolysis affords camphoric acid [T]- Camphoric acid is converted to camphor as described in Route I. 

Birch reduction11 is the partial reduction of aromatic rings by solvated electrons produced when alkali metals dissolve (and react) in liquid amines. Typical conditions are sodium in liquid ammonia or lithium in methylamine. These electrons add to benzene rings to produce, probably, a dianion 57 that is immediately protonated by a weak acid (usually a tertiary alcohol) present in solution. The anions in the supposed intermediate 57 keep as far from each other as they can so the final product is the non-conjugated diene 58. It is important to use the blue solution of solvated electrons before it reacts to give hydrogen and NaNH2. 

The partial reduction of a benzene ring by sodium or lithium in liquid ammonia. The products are usually cyclohexa- 1,4-dienes, (p. 797)... 

The partial reduction of the triple bond of lithium ynoiates 173 by activated LiH provides the lithium ii-enolates 174 derived from aldehydes (equation 70) °. This is a useful reaction, since these enoiates of aldehydes are not easily prepared by the usual base treatment of aldehydes. Activated LiH is prepared in situ from cyclohexa-1,3-diene and lithium tetramethylpiperazide or from cyclohexa-1,3-diene and BuLi. The superactive LiH, prepared from hydrogen with BuLi-tetramethylethylenediamine, can also be used. ... 

Birch reduction is a partial reduction of aromatic compounds by electron transfer from dissolving metals—usually Na in liquid ammonia or Li in ethylamine—in the presence of a weak proton donor—usually an alcohol. The reaction behaves as if dianion (30) were an intermediate, giving non-conjugated dienes (31). Electron-donating substituents repel the anions (32) to give products like (33). whilst electron-withdrawing substituents attract the anions (34), to give products like (35). 

The skipped di- or triynes are reduced to skipped (Z,Z)-dienes or (Z,Z,Z)-trienes by partial reduction with NaBH4/Ni(OAc)2 4H2O (equation 111). 

A mixture of cycloocta-l,3,5-triene and cycloocta-l,3,6-triene formed by partial reduction of cyclooctatetraene is the usual starting point for the study of cyclooctatriene complexes, and obviously complexes may be derived from both isomers. Also, the 1,3,5-isomer is in thermal equilibrium with its valence tautomer, bicyclo[4.2.0]octa-2,4-diene (XXVII), at 100° C (30), from which complexes may also be formed. Although silver nitrate... 

Zinc pyridine acetic acid Partial reduction of dienes to ethylene derivatives... 

Preparation from Methyl Santalbate. Adlof prepared gram quantities of methyl (9Z,ll )-[9,10- H]-octadecadienoate using methyl santalbate [methyl ( )-octadec-ll-en-9-ynoate] obtained from Santalum album seeds (12). Partial reduction of the triple bond of methyl ( )-octadec-ll-enynoate in the presence of Lindlar catalyst, quinoline, and deuterium gas gave the (Z, ) conjugated diene system (Fig. 6.1). 

An interesting example of the synthetic utility is the partial reduction of compound 14 under standard Birch conditions to give the diene 15, and after acid hydrolysis the exo-enone 16, of difficult access by other methodologies (Scheme 13.7) [8]. 

Decomplexation may be achieved by oxidation. Trimethylamine-N-oxide and cerium(IV) are commonly used reagents for this. Complexes of electron-poor dienes may be photochemically decomplexed in the presence of acetic acid (Scheme 10.2). This proceeds with partial reduction." ... 

The synthesis of enynes is of interest in the chemistry of certain natural products. Terminal enynes occur in several natural products such as histrionicotoxin and laurencin, and the internal enyne unit is found along with polyacetylenes and allenes in natural products from Compositae and Umbelliferae. Both internal Z-and. E-enynes are also useful as precursors to stereochemically define d dienes on their partial reduction. A group from Phillips-Duphar has described an efficient synthesis of the functionalized enyne (95), which serves as the C5 synthon for the convergent synthesis of vitamin A. The l,3-dichloro-2-ether (94) is dechlorinated, substituted, and isomerized in one step on reaction with two molar equivalents of sodium acetylide in liquid ammonia, giving (95) with an E Z ratio... 

Meinwalda, J. (2005) Location of double bonds in diene and triene acetates by partial reduction followed by methylth-... 

In their efforts to prepare a [D4]-labeled p4t-neuroprostane, the Galano group carried out partial reduction of the skipped diyne substrate in order to access the Z,Z,Z-triene moiety of the final product (Fig. 12) [34]. While Lindlar s catalyst provided a mixture of mono-reduction of the less hindered alkyne (with the ethyl substituent), the desired triene as well as over-reduced diene product, P-2 nickel yielded a much cleaner conversion to the desired product with 98% purity. The product was then transformed into the target molecule by a sequence of TBAF deprotection of the TBS ether and saponification. 

Industrial synthesis of vitamin A (Hoffman-La-Roche) goes through partial hydrogenation of an enyne (equation 161)277. A number of syntheses of pheromones, where the reduction of an enyne to a diene is the key step, have been devised. A few selected examples are given in Table 29278. During the total synthesis of endiandric acids, Nico-laou employed hydrogenation of a polyenyne intermediate with a Lindlar catalyst to generate an intermediate which underwent symmetry-allowed cyclizations to result in the natural product (equation 162)279. 

Ffirai and Toshima have published several reports on the synthesis of transition-metal nanoparticles by alcoholic reduction of metal salts in the presence of a polymer such as polyvinylalcohol (PVA) or polyvinylpyrrolidone (PVP). This simple and reproducible process can be applied for the preparation of monometallic [32, 33] or bimetallic [34—39] nanoparticles. In this series of articles, the nanoparticles are characterized by different techniques such as transmission electronic microscopy (TEM), UV-visible spectroscopy, electron diffraction (EDX), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) or extended X-ray absorption fine structure (EXAFS, bimetallic systems). The great majority of the particles have a uniform size between 1 and 3 nm. These nanomaterials are efficient catalysts for olefin or diene hydrogenation under mild conditions (30°C, Ph2 = 1 bar)- In the case of bimetallic catalysts, the catalytic activity was seen to depend on their metal composition, and this may also have an influence on the selectivity of the partial hydrogenation of dienes. 

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