Friedel-Crafts alkylation discovery

Roberts, R. M. Khalaf A. A. (Eds.), Friedel-Crafts Alkylation Chemistry A Century of Discovery, Marcel Dekker, New York, 1984. 

Two years after the discovery of the first asymmetric Br0nsted acid-catalyzed Friedel-Crafts alkylation, the You group extended this transformation to the use of indoles as heteroaromatic nucleophiles (Scheme 11). iV-Sulfonylated aldimines 28 are activated with the help of catalytic amounts of BINOL phosphate (5)-3k (10 mol%, R = 1-naphthyl) for the reaction with unprotected indoles 29 to provide 3-indolyl amines 30 in good yields (56-94%) together with excellent enantioselec-tivities (58 to >99% ee) [21], Antilla and coworkers demonstrated that A-benzoyl-protected aldimines can be employed as electrophiles for the addition of iV-benzylated indoles with similar efficiencies [22]. Both protocols tolerate several aryl imines and a variety of substituents at the indole moiety. In addition, one example of the use of an aliphatic imine (56%, 58% ee) was presented. 

Shortly after the discovery of the first asymmetric phosphoric acid-catalyzed transformation of enecarbamates, Zhou et al. expanded the scope of the Friedel-Crafts alkylation of indoles 29 with electron-rich alkenes to enamides 127 (Scheme 51) [74],... 

Study of the reactivity of aromatic C-H bonds in the presence of transition metal compounds began in the 1960s despite the quite early discovery of Friedel-Crafts alkylation and acylation reactions with Lewis acid catalysts. In 1967, we reported Pd(II)-mediated coupling of arenes with olefins in acetic acid under reflux [1], The reaction involves the electrophilic substitution of aromatic C-H bonds by a Pd(II) species, as shown in Scheme 2, and this is one of the earliest examples of aromatic C-H bond activation by transition metal compounds. Al-... 

As indicated from computational studies, the catalyst-activated iminium ion MM3-2 was expected to form with only the (E)-conformation to avoid nonbonding interactions between the substrate double bond and the gem-dimethyl substituents on the catalyst framework. In addition, the benzyl group of the imidazolidinone moiety should effectively shield the iminium-ion Si-face, leaving the Re-face exposed for enantioselective bond formation. The efficiency of chiral amine 1 in iminium catalysis was demonstrated by its successful application in several transformations such as enantioselective Diels-Alder reactions [6], nitrone additions [12], and Friedel-Crafts alkylations of pyrrole nucleophiles [13]. However, diminished reactivity was observed when indole and furan heteroaromatics where used for similar conjugate additions, causing the MacMillan group to embark upon studies to identify a more reactive and versatile amine catalyst. This led ultimately to the discovery of the second-generation imidazolidinone catalyst 3 (Fig. 3.1, bottom) [14],... 

Early research on hydrothermal reactions was also carried out by Charles Friedel, an instructor at the Ecole Normale Supdrieure [108], the same institution where Paul Villard received his education. Over many years Charles, and later his son Georges Friedel, published a series of papers on the reaction of minerals in H2O at temperatures and presumably also pressures far above critical, starting with the preparation of quartz in 1879 [109,110]. Charles Friedel is more famous for his discovery of the Friedel-Crafts alkylation of aromatics. The works of de LaTour, Daubr6e and the Friedels together ensured that the first experimental reactions of and in SCFs were those of H2O, as reviewed in great detail by Morey [111]. 

Friedel-Crafts alkylation is one of the most frequently used and widely studied reactions in organic chemistry. Since the initial discovery by Charles Friedel and James Mason Crafts in 1877, a large number of applications have emerged for the construction of substituted aromatic compounds. Friedel-Crafts alkylation processes involve the replacement of C—H bond of an aromatic ring by an electrophilic partner in the presence of a Lewis acid or Bronsted acid catalyst. Particularly, catalytic asymmetric Friedel-Crafts alkylation is a very attractive, direct, and atom-economic approach for the synthesis of optically active aromatic compounds. However, it took more than 100 years from the discovery of this reaction until the first catalytic asymmetric Friedel-Crafts (AFC) alkylation of naphthol and ethyl pyruvate was realized by Erker in 1990. Nowadays, owing to continued efforts in developing... 

After the discovery that Friedel-Crafts alkylations and acylations involve cationic electrophiles, it was realized that the same reactions can be accomplished by other combinations of reagents and catalysts. We study two of these reactions generation of carbocations from alkenes and from alcohols. 

In 1877, Charles Friedel and James Mason Crafts [30a, b] corporately discovered that treatment of amyl chloride with aluminum strips in benzene led to the formation of amylben-zene. This type of transformation was found to be general for alkyl halides and aromatics under the catalysis of Lewis acid. Along with the discovery of the closely related acylation [30c, d], these two men are best remembered by Friedel-Crafts reaction that bears their names. With various modem modifications that appeared in the Uterature, including enan-tioselective variants [31], Friedel-Crafts alkylation and acylation have already become one of the most powerful C—C bond forming reactions in organic chemistry [32]. These methods are recognized to date as of fundamental importance not only in acadania but also in industry [33]. As shown in Scheme 10.18, some heteroaromatics, instead of the aryl component or alcohol, and alkenes instead of halides can be used as suitable substrates. Also, other common Lewis acids like BFj, TiCl, SnCl, ScfOTOj, etc., and Brpnsted acids snch as HF, H SO, and superacids (e.g., HF SbFj, HS03-SbFj) can also used as catalysts. 

At the time the chemistry of (OC)9Co3CCO+PF6 was being developed (27, SO), another route to this novel acylium ion was found in these laboratories (31, 32). This discovery was a result of our intention to adapt the Friedel-Crafts synthesis of benzylidynetricobalt nonacarbonyl complexes of Dolby and Robinson (15) to the preparation of alkyl derivatives of methylidynetricobalt nonacarbonyl, whose general preparation was not well in hand. The reaction chosen for investigation was the aluminum chloride-induced interaction of tetraalkyltin compounds with ClCCo3(CO)9 In analogy to a known ketone synthesis (33),... 

The retro-synthetic analysis ouflined in Scheme 6.1 shows that in addition to the Pictet-Spengler route previously used by discovery, several others are also possible. The Bischler-Napieralski condensation of 5-methyltryptamine and 2-cyclohexylacetic acid chloride as well as the Friedel-Crafts reaction of the N-protected 5-methyltryptamine allows preparation of the prochiral imine derivative 7. The 2-cyclohexylmethyl side chain may also be introduced via alkylating an unsubstituted THpC by 2-cyclohexylmethyl chloride. As shown in Scheme 6.1, all of these routes involve 5-methyltryptamine as a common building block. 

The catalytic alkylation of saturated hydrocarbons and olefins was discovered in 1932 by Ipatieff and Pines. They employed conventional Friedel-Crafts catalyst, i.e., promoted aluminum chloride. The use of sulfuric acid as a catalyst was discovered by Birch and Dunstan in 1936. Promptly after the latter discovery, the reaction was commercialized to produce high-octane aviation gasoline from isobutane and butylenes employing not only sulfuric acid but anhydrous hydrofluoric acid. The processes were expanded rapidly during World War II to supply aviation gasoline. By the end of the war, 59 alkylation plants existed in this country with a rated capacity of... 

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