Alkenes side-chain alkylation with

The side chain alkylation of alkyl benzenes is usually performed with alkenes as alkylating agents in the presence of strong-acid catalysts (256,257). The use of highly basic catalysts such as alkali metals, their hydrides, and sodium and potassium complexes for alkylation of alkylaromatic hydrocarbons has also been reported (256,257). The reaction mechanism proposed by Pines et al. (258) involves the addition of a benzylic carboanion to the alkene (Scheme 41). 

Alkenes may also be used as reagents in side-chain alkylation. Zeolites with occluded alkali metal and alkali metal oxide clusters were tested in alkylation of toluene with ethylene439 440 Alkali metal clusters created by decomposing Na or... 

The 3//-l,2-benzodithiolan-3-one 377 (Scheme 70) having the reactive alkene side-chain with the role of the C(6)=C(7) double bond in leinamycin 5 (Scheme 69) has been synthesized, as a highly simplified structural analogue of antitumor antibiotic leinamycin 5 <2003JA4996, 2002JOC9054>. Reaction of 5 with thiols, as shown, affords, via several intermediates, involving 375, an episulfonium ion 376, which subsequently participates in DNA alkylation processes. 

Liquid-phase side-chain alkylation of alkylaromatics with alkenes proceeds over NaNs/zeolite (59) and Na/Na0H/Al203 (33). Alkylation of o-xylene with butadiene over Na/K2C03 yields o-tolylpent-2-ene, which is a precursor for 2,6-dimethylnaphthalene (116). 

Pb(C2H5)4 is used as a catalyst for side-chain alkylation of toluene with ethene [731], for the reaction of alkenes with SO2 [635], for the halogenation of alkanes such as ethane, propane, or pentane in the gas and liquid phase [123, 650], for vulcanizing a mixture of acetaldehyde copolymers with acrolein or other unsaturated compounds, and a natural rubber [858], for curing caoutchouc [629], and for the polymerization of rosin or rosin acid derivatives [493, 704]. Pb(C2H5)4 is part of room-temperature, light-vulcanizable silicone rubber compositions [875]. 

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

A modified version of the Brown-Negishi reaction using B-alkylcatechol-boranes was reported (Scheme 32). This novel method is based on a simple one-pot procedure involving the hydroboration of various substituted alkenes with catecholborane, followed by treatment with catalytic amount of oxygen/DMPU/water and a radical trap. Efficient radical additions to a,ft-unsaturated ketones and aldehydes have been reported. Primary alkyl radicals are efficiently generated by this procedure and the reaction has been applied to a 300 mmol scale synthesis of the y-side chain of (-)-perturasinic... 

Addition of carbenes to Jt-electron excessive aromatic compounds, or those which possess a high degree of bond fixation, is well established. Dihalocarbenes react with naphthalenes with ring expansion to produce benztropylium systems (Scheme 7.8). Loss of hydrogen halide from the initially formed product leads to an alkene which reacts with a second equivalent of the carbene to yield the spirocyclopropyl derivatives in high yield (>95%) [14, 50]. Insertion into the alkyl side chain (see Section 7.2) also occurs, but to a lesser extent [14]. Not unexpectedly, dichlorocarbene adds to phenanthrenes across the 9,10-bond [9, 10, 14], but it is remarkable that the three possible isomeric spiro compounds could be isolated (in an overall yield of 0.05% ) from the corresponding reaction with toluene [14]. 

Plant sterols such as stigmasterol typically contain an extra ethyl group when compared with cholesterol. Now this is not introduced by an electrophilic ethylation process instead, two successive electrophilic methylation processes occur, both involving SAM as methyl donor. Indeed, it is a methylene derivative like that just seen in ergosterol formation that can act as the alkene for further electrophilic alkylation. After proton loss, the product has a side-chain with an ethylidene substituent the side-chains of the common plant sterols stigmasterol and sitosterol are then related by repeats of the reduction and dehydrogenation processes already seen in ergosterol formation. 

Triple bonds in side chains of aromatics can be reduced to double bonds or completely saturated. The outcome of such reductions depends on the structure of the acetylene and on the method of reduction. If the triple bond is not conjugated with the benzene ring it can be handled in the same way as in aliphatic acetylenes. In addition, electrochemical reduction in a solution of lithium chloride in methylamine has been used for partial reduction to alkenes trans isomers, where applicable) in 40-51% yields (with 2,5-dihydroaromatic alkenes as by-products) [379]. Aromatic acetylenes with triple bonds conjugated with benzene rings can be hydrogenated over Raney nickel to cis olefins [356], or to alkyl aromatics over rhenium sulfide catalyst [54]. Electroreduction in methylamine containing lithium chloride gives 80% yields of alkyl aromatics [379]. 

Condensation of ester (44e) with the anion of malononitrile gave the alkene (44g) <91JPR35>. Oxadiazole (43e) and triethyl phosphite gave a methane phosphate which underwent a Wittig reation with aldehydes ArCHO to form alkenes (43f). When the alkyl side chain contained an active methylene group, as in (43g), reaction with arenediazonium salts ArN2X yielded arylhydrazones (43h) <88LA909>. 

Oxidation of Other Arenes. Aromatic compounds with longer alkyl side chains can be converted to ketones or carboxylic acids. All the previously discussed reagents except Cr02Cl2 usually afford the selective formation of ketones from alkyl-substituted arenes. Oxidation with Cr02Cl2 usually gives a mixture of products. These include compounds oxidized in the P position presumably formed via an alkene intermediate or as a result of the rearrangement of an intermediate epoxide.110,705... 

In a similar but more complex reaction, dienes carrying a (3-diketo side chain have been alkylated with various vinyl bromides and cyclized to the corresponding alkylated cyclopropyl alkenes in the presence of silver carbonate (Scheme 10.27). With a relative cis stereochemistry for the newly created C-C bonds, the mechanism is... 

The red-sided garter snake pheromone components were isolated by hexane extraction of the skin lipids of sacrificed snakes. Female snakes yielded more total lipid than males (38.4 versus 8.4mg snake-1)80 Initial fractionation on an activity III alumina column gave a fraction (eluted with 98 2, hexanes ethyl ether) that was attractive to courting males. NMR and infrared (IR) spectra of this fraction were suggestive of the presence of methyl ketones, straight chain alkyl lipid subunits, and Z-alkenes. GC—MS analysis, including extensive consideration of the fragmentation of the electron impact MS data, led to the identification of a family of relatively nonvolatile (C29—C37) lipid methyl ketones. Specifically, the individual components of a mixture of saturated and monounsaturated methyl ketones 18—30 were identified. 

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