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Friedel-Crafts alkylation See

Carbocations also feature as intermediates in electrophilic addition reactions (see Section 8.1) and in Friedel-Crafts alkylations (see Section 8.4.1). [Pg.217]

It was reported that Sc(OTf)3 catalyzes Diels-Alder reactions in [bmim][X] (X = BF4, SbFg or OTf), in this case at much lower catalyst loadings (0.2 m%). In contrast to the Friedel-Crafts alkylation (see below) the product did not form a separate phase and was recovered by extraction with ether. It was shown, however, that the ionic liquid containing the catalyst could be recycled eleven times without loss of activity, Scheme 4. Furthermore, improved endojexo selectivities were observed with cyclic dienes. [Pg.161]

Another category of reductions involves aryl ketones. The Friedel-Crafts acylation reaction reacts benzene with an acid chloride such as butanoyl chloride (49) to give an aryl ketone, 50. Complete removal of the oxygen from this ketone constitutes a method to make straight-chain arenes, which cannot be prepared via Friedel-Crafts alkylation (see Section 21.3.2). At least two classical methods are used to accomplish this reaction, which is formally a reduction. If 50 is treated with zinc metal in HCl, the product is 1-phenylbutane, 105. This acidic reduction involves a mineral acid such as HCl and an active metal, and it is called the Clemmensen reduction. [Pg.1066]

We will show here the classification procedure with a specific dataset [28]. A reaction center, the addition of a C-H bond to a C=C double bond, was chosen that comprised a variety of different reaction types such as Michael additions, Friedel-Crafts alkylation of aromatic compounds by alkenes, or photochemical reactions. We wanted to see whether these different reaction types can be discerned by this... [Pg.193]

From what has been said thus far, it is evident that the electrophile in Friedel-Crafts alkylation is a carbocation, at least in most cases. This is in accord with the knowledge that carbocations rearrange in the direction primary — secondary —> tertiary (see Chapter 18). In each case, the cation is formed from the attacking reagent and the catalyst. For the three most important types of reagent these reactions are... [Pg.710]

For a monograph, see Roberts, R.M. Khalaf, A.A. Friedel-Crafts Alkylation Chemistry Marcel Dekker NY, 1984. For a treatise on Friedel-Crafts reactions in general, see Olah, G.A. Friedel-Crafts and Related Reactions Wiley NY, 1963-1965. Volume 1 covers general aspects, such as catalyst activity, intermediate complexes, and so on. Volume 2 covers alkylation and related reactions. In this volume the various reagents are treated by the indicated authors as follows alkenes and alkanes, Patinkin, S.H. Friedman, B.S. p. 1 ... [Pg.747]

See Davister, M. Laszlo, P. Tetrahedron Lett., 1993, 34, 533 for examples of paradoxical selectivity in Friedel-Crafts alkylation. [Pg.748]

These alkylation and acylation reactions are important because Friedel-Crafts alkylation and acylation (11-12, 11-14) cannot be applied to most nitrogen heterocycles. See also 13-15. [Pg.934]

Friedel-Crafts alkylation of benzene or toluene by allyl chloride in presence of ethylaluminium chlorides is vigorous even at — 70°C, and explosions have occurred. See Lewis acids, etc., next below... [Pg.419]

Other electrophilic substitution reactions on aromatic and heteroaromatic systems are summarized in Scheme 6.143. Friedel-Crafts alkylation of N,N-dimethyl-aniline with squaric acid dichloride was accomplished by heating the two components in dichloromethane at 120 °C in the absence of a Lewis acid catalyst to provide a 23% yield of the 2-aryl-l-chlorocydobut-l-ene-3,4-dione product (Scheme 6.143 a) [281]. Hydrolysis of the monochloride provided a 2-aryl-l-hydroxycyclobut-l-ene-3,4-dione, an inhibitor of protein tyrosine phosphatases [281], Formylation of 4-chloro-3-nitrophenol with hexamethylenetetramine and trifluoroacetic acid (TFA) at 115 °C for 5 h furnished the corresponding benzaldehyde in 43% yield, which was further manipulated into a benzofuran derivative (Scheme 6.143b) [282]. 4-Chloro-5-bromo-pyrazolopyrimidine is an important intermediate in the synthesis of pyrazolopyrimi-dine derivatives showing activity against multiple kinase subfamilies (see also Scheme 6.20) and can be rapidly prepared from 4-chloropyrazolopyrimidine and N-bromosuccinimide (NBS) by microwave irradiation in acetonitrile (Scheme... [Pg.201]

Aromatic compounds, 13 108-109 13 680. See also Aromatics acylation of, 12 173-181 amination of, 12 184 arylation of, 12 170-171 Cycloalkylation of, 12 169 in diesel fuel, 12 425 formylation of, 12 178 Friedel-Crafts acylation of, 12 174 Friedel-Crafts alkylation of, 12 164 nitration of, 12 182-183 oxidative coupling of, 19 654 sulfonation of, 12 181 sulfonation reagents for, 23 521-524 Aromatic-containing polymers, sulfonation of, 23 535-536... [Pg.70]

In chemistry, the term complex can mean many things. The belief, which I shared, that complexes of the metal halides with monomers or with alkyl halides are important in CP induced me to undertake several difficult but fruitful investigations. Complexes between RX and MtXn were well known [see References in [24]] and they were being studied at about that time by several workers, such as H. C. Brown at Purdue University with regard to the A1 halides and Fairbrother at Manchester University was concerned with similar systems and with the ionisation of trityl halides by metal halides. I was concerned with TiCl4, my then favourite catalyst , and its interaction with the alkyl chlorides which were used as solvents for CP. The theory first suggested by Pepper [46] and adopted by us was that if a CP was initiated in an alkyl chloride RC1, and there was no evident effect of water, then the initiation was most likely akin to a Friedel-Crafts alkylation. This was represented by the equations (7) and (8) ... [Pg.30]

However, although we invoked a Lewis acid complex to provide the halonium electrophile, there is considerable evidence that, where appropriate, the electrophile in Friedel-Crafts alkylations is actually the dissociated carbocation itself. Of course, a simple methyl or ethyl cation is unlikely to be formed, so there we should assume a Lewis acid complex as the electrophilic species. On the other hand, if we can get a secondary or tertiary carbocation, then this is probably what happens. There are good stereochemical reasons why a secondary or tertiary complex cannot be attacked. Just as we saw with Sn2 reactions (see Section 6.1), if there is too much steric hindrance, then the reaction becomes SnI type. [Pg.306]

This involvement of carbocations actually limits the utility of Friedel-Crafts alkylations, because, as we have already noted with carbocations, rearrangement reactions complicate the anticipated outcome (see Section 6.4.2). For instance, when a Lewis acid... [Pg.307]

To be really satisfactory, a Friedel-Crafts alkylation requires one relatively stable secondary or tertiary carbocation to be formed from the alkyl halide by interaction with the Lewis acid, i.e. cases where there is not going to be any chance of rearrangement. Note also that we are unable to generate carboca-tions from an aryl halide - aryl cations (also vinyl cations, see Section 8.1.3) are unfavourable - so that we cannot nse the Friedel-Crafts reaction to join aromatic gronps. There is also one further difficulty, as we shall see below. This is the fact that introduction of an alkyl substitnent on to an aromatic ring activates the ring towards fnrther electrophilic substitution. The result is that the initial product from Friedel-Crafts alkylations is more reactive than the... [Pg.308]

A similar problem of complex formation may be encountered if either amino or phenol groups are present in the substrate, and the reaction may fail. Under such circumstances, these groups need to be blocked (protected) by making a suitable derivative. Nevertheless, Friedel-Crafts acylations tend to work very well and with good yields, uncomplicated by multiple acylations, since the acyl group introduced deactivates the ring towards further electrophilic substitution. This contrasts with Friedel-Crafts alkylations, where the alkyl substituents introduced activate the ring towards further substitution (see Section 8.4.3). [Pg.309]

The formation of carbon-carbon bonds by electrophilic attack on the n system is an important reaction in aromatic chemistry, with both Friedel-Crafts alkylation and acylation following this pattern (see Chapter 11). There also are valuable synthetic procedures in which carbon-carbon bond formation results from electrophilic attack by a carbocation on an alkene. The reaction of a carbocation with an alkene to form a new carbon-carbon bond is both kinetically accessible and thermodynamically favorable because a n bond is replaced by a stronger [Pg.596]

Subsequent intramolecular Friedel-Crafts alkylation and elimination yields the coumarin derivatives (See Scheme 14, Sect. 2.2). With 5 mol% of BiCl3, the desired products 21a-d have been obtained in high yields after short reaction times (1-2 h) (Scheme 17). [Pg.127]


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Friedel Crafts alkylation

Friedel-Crafts alkylations

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