Alkyl derivatives dienes

Alkyl derivatives of 1,3-butadiene usually undergo photosensitized Z-E isomerism when photosensitizers that can supply at least 60 kcal/mol are used. Two conformers of the diene, the s-Z and s-E, exist in equilibrium, so there are two nonidentical ground states from which excitation can occur. Two triplet excited states that do not readily interconvert are derived from the s-E and s-Z conformers. Theoretical calculations suggest that at their energy minimum the excited states of conjugated dienes can be described as an alkyl radical and an orthogonal allyl system called an allylmethylene diradical ... 

Most of the alkylations were carried out by adding a solution of 3,3-ethylenedioxypregna-5,16-dien-20-one in tetrahydrofuran to a solution of lithium in liquid ammonia to the point of color discharge. Treatment with the alkyl halide then furnishes the corresponding 17a-alkyl derivative (10). After hydrolysis of the 3-ketal group, 17a-methyl-, ethyl-, propyl-, butyl-, hexyl-, octyl-, allyl-, and benzylprogesterones are obtained. 

Alkyl derivatives of the alkaline-earth metals have also been used to initiate anionic polymerization. Organomagnesium compounds are considerably less active than organolithiums, as a result of the much less polarized metal-carbon bond. They can only initiate polymerization of monomers more reactive than styrene and 1,3-dienes, such as 2- and 4-vinylpyridines, and acrylic and methacrylic esters. Organostrontium and organobarium compounds, possessing more polar metal-carbon bonds, are able to polymerize styrene and 1,3-dienes as well as the more reactive monomers. 

Most of these compounds show a limited solubility in non-polar solvents. In addition, the respective alkyl derivatives are rather unstable in solution and decompose easily [297]. The peculiarity about CpNd complexes is their ability to polymerize various alkenes such as a-olefines, styrene, c -dienes as well as polar acrylates [298,299]. 

Azo compounds like esters or imides of azo dicarboxylic acid act as reactive dienophiles in normal electron demand hetero Diels-Alder reactions due to the strong activation caused by two electron-withdrawing moieties. In the last years, considerable attention has focused on alkyl and phenyl derivatives of 1,2,4-tria-zoline-3,5-diones since their cycloadditions to chiral dienes proceed with often excellent facial selectivities. Thus, when reacting an oxapropellane derived diene with N -methyltriazolinedione, Paquette et al. obtained the cycloadduct as single diastereomer, but both maleic anhydride and N-phenyl maleimide were distinctly less reactive and turned out to undergo cycloadditions with poor selectivities [289]. 

The cycloaddition reaction is applicable to various derivatives of 3-trimethylsilyloxy-1,3-diene, including 1-alkyl derivatives, thus providing stereoselective routes to various derivatives of 4-pyranone. ... 

Ziegler-Naita caialysts consist of a combination of alkyls or hydrides of Group I-III metals with salts of the Group IV-VHI metals. The most generally efficient catalyst combinations are those in which an aluminum alkyl derivative is interacted with titanium, vanadium, chromium or zirconium salts. The most important application of these catalysts is in the polymerization of olefins and conjugated dienes. Not every catalyst combination is equally effective in such polymerizations. As a general rule, Ziegler-Natta combinations that will polymerize 1-olefins will also polymerize ethylene, but the reverse is not true. 

Glucose-derived diene (451) displays a notable diastereofacial bias on addition to dienophiles. Its preparation relies on the alkylation of tetraacetylglucopyranosyl brcmiide (450) with sodium salt (449) followed by 0-silylation of the resulting enone (Scheme 106). "... 

For the preparation of unsymmetrical ferrocenes, two ways by which only mono-substituted derivatives are produced have been suggested. One route starts from iron tetracarbonyl and a substituted cyclopenta-diene the other from monocyclopentadienyl iron dicarbonyl bromide, which on treatment with a substituted cyclopentadienyl lithium is finally converted into the corresponding mono-substituted ferrocene. Experience shows the first method to be more suitable for the preparation of aryl, and the latter method for the preparation of alkyl, derivatives (57). Corresponding work already carried out on substitution in Ru(C5H6)2 and Os CsH5)2 has also been fruitful. It is found that in the Friedel-Crafts reaction with acetyl or benzoyl chloride there is a distinct predominance of mono- over disubstitution as the atomic weight of the central atom increases (47, 72). 

Dienes also can alkylate arenes to give products which are generally cyclic. For example, isoprene reacts with 1,2,4-trimethylbenzene in the presence of H2SO4 to give an indane derivative (equation 91). A large number of phenols have been used for alkylations with dienes. The products are either allylated phenols, or products derived by further ring closure of the phenolic oxygen with the side chain derived from the diene. 

Relatively little work has been reported on the acylation of 1-trialkylsilyl-1,3-butadienes. As is observed with vinylic substrates, the regioselectivity of reaction can be controlled by substituents other than the silyl group. For example, acylations of 3-alkyl derivatives are controlled by the relative stability of the tertiary carbenium ion following attack of the electrophile at the C-4 terminus (Scheme 17). Silicon is retained in both the immediate chloride addition product, and the diene formed by subsequent base-catalyzed eliminations. ... 

A study of DNA adducts of alkylated PtCl(dien) derivatives showed that the extent of DNA repair in higher alkylated platinum derivatives is... 

Furan (282) can be alkylated a to the SO2 group, but a mixture of mono- and bis-alkylation products is always obtained. Alkene (290b) did not cyclize on heating and the sulfolene-derived diene moiety was unreactive towards intramolecular Diels-Alder cyclization, even following reaction of the furan moiety with dienophiles. However, dienophiles (291a/b) were more reactive and cyclized via (292a/b), which were formed in situ by reversible reaction of the furan with methylvinyl ketone [3] (Scheme 6.83). 

The structures of 2-pyridone and itsA -alkyl derivatives suggest that they could perform as dienes in Diels-Alder reactions. When maleic anhydride and /V-methyl-2-pyridone are heated alone or in toluene at 100" a 2 1 adduct is formed (24%) that dissociates into the pyridone and maleic anhydride in polar solvents or when heated to its melting point or when sublimed. The structure... 

Various transition metal salts, in the presence of alkyl derivatives, constitute the Ziegler catalyst systems that are also capable of reducing monoenes, dienes, and aromatic substrates. A variety of aromatic compounds, such as benzene, naphthalene, phenol, or xylenes, can be efficiently converted into saturated cycloalkanes with the Ziegler catalyst Et3Al/Ni(2-ethylhexanoate)2 at 75 atm and elevated temperature (150-200°C) (96). The analogous Et3Al/Co(2-ethyUiexanoate)2 system reduces phenol to cyclohexanol, with selectivity higher than 90% at 40 atm and 25°C. 

Friedel-Crafts alkylations of arenes with mesylates, benzyl or allyl alcohols, aldehyde/diol combinations (reductive alkylation), FS-dienes, or alkenes in an ionic liquid are also effectively catalyzed by Sc(OTf)3. Sc(OTf)3 works as an efficient catalyst for the condensation reaction of trimethylhydroquinone with isophytol to afford a-tocopherol. 2-Aminoalkylation of phenols with a-iminoacetates (or glyoxylate/amine) is catalyzed by Sc(OTf)3 to produce amino acid derivatives. The Sc(OTf)3-catalyzed alkylations of indoles with a-hydroxy esters, aziri-dines, acetals, and aldehydes have been utilized as key steps of total s)mtheses as exemplified in eq 15. ... 

N-Alkyl Derivatives. - Isomeric mixtures of AT-(hexosid-2-yl)-pyrrolidine derivatives, e.g. 98, were formed along with some AT-demethylated amine 99 on treatment of the AT-oxide 100 with lithium diisopropylamide in the presence of various dienes, e.g. 2-methyl-1,4-butadiene. The synthesis of carbocyclic analogues of a mannose trisaccharide, linked via nitrogen atoms, is covered in Chapter 18. 

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