Aromatic direct allylation

The direct allylation of aromatic compounds with allylic chlorides is achieved in the presence of a catalytic amount of indium metal. According to the authors, indium is considered to act as a Lewis acid (Equation (101)).399 Trialkylindiums react with acid chlorides to give ketones. When trialkylindiums are treated with air prior to the reaction with acid chlorides, esters are formed (Scheme 121).400 The reaction of cyclopentadienylindium(i) with aldehydes in aqueous media gives mixtures of the isomeric coupling products (Equation (102)).401... 

Mechanistically, this sequence can be rationalized by initial alkynone formation upon coupling of acid chloride 7 and aUcyne 4 furnishing the alkynone 8, which now can act as a dipolarophile (Scheme 18). The amount of triethylamine is sufficient to deprotonate the l-(2-oxoethyl)pyridinium bromide 25 giving rise to the zwitter-ionic pyridinium ylide 27, an allyl-type dipole suitable for the subsequent 1,3-dipolar cycloaddition to give the dihydroindolizine 28. Under either aerobic or anaerobic conditions in the final cycloaddition step oxidative aromatization directly furnishes the desired indolizines 26. 

Furoquinoline alkaloids specifically labeled with 14C in the furan ring were required for biosynthetic studies (see Section VII of this chapter), and since existing routes produced low yields, Grundon and co-workers (195, 196) developed a more efficient synthesis from 4-methoxy-3-prenyl-2-quinolones 244-246. These compounds had previously been prepared from aromatic amines and substituted malonates, but direct allylation is more suitable for the preparation of labeled compounds, employing, for example, [14C]-3,3-dimethylallyl bromide. It was found that reaction of... 

The direct allylation of aromatic compounds such as benzene, toluene, p-jylene, anisole, phenol, and heterocycles was performed by Nishibayashi using allylic alcohol and bridged dirutheniun complexes. ... 

Tertiary Amines.— The co-ordinating properties of tertiary aliphatic nitrogen atoms have once again been made use of for the directed metallation of aromatic and allylic systems. Although several examples of ortho-palladated... 

Catalytic amounts of I fCl4-AgC104 and Hf(OTf)4 are used for activation of acid halides and acid anhydrides for Friedel -Crafts acylation (Scheme 42) 178 the reactions of both reactive and unreactive aromatic substrates proceed smoothly in the presence of Hf(OTf)4. Furthermore, the Fries rearrangement179,180 and direct C-acylation of phenolic compounds181,182 take place using Hf(OTf)4. Formation of esters and Mannich-type reactions and allylation of imines have been also reported.152... 

Rhodium catalysts have also been used with increasing frequency for the allylic etherification of aliphatic alcohols. The chiral 7r-allylrhodium complexes generated from asymmetric ring-opening (ARO) reactions have been shown to react with both aromatic and aliphatic alcohols (Equation (46)).185-188 Mechanistic studies have shown that the reaction proceeds by an oxidative addition of Rh(i) into the oxabicyclic alkene system with retention of configuration, as directed by coordination of the oxygen atom, and subsequent SN2 addition of the oxygen nucleophile. 

The stars were characterized by GPC (LLS) and NMR spectroscopy. The RI traces (see Fig. 5) showed the formation of monomodal narrow dispersity stars. Molecular characteristics of two representative samples are summarized in Table 2. According to NMR evidence (Fig. 6), the arms were quantitatively functionalized with allyl groups. The end-functionality of the stars was calculated by comparing the integrated peak area of the core protons [aromatic (5= 6.82 ppm), -CH2- (6=4.0 ppm)] and chain end allyl protons (-CH2- (5=2.0 ppm), -CH= (5=5.8 ppm), =CH2 (5=5.1 ppm), and was found to be 8.1, after correcting for the presence of -10% linear contaminant. Quantitative allyl-functionalization is direct proof for the formation of the octa-arm stars. 

Two methods for the direct construction of enantiomerically-enriched allylic amines have recently been reported. John Hartwig of Yale University has developed (Angew. Chem. Int. Ed. 2004,43,4797) an Ir complex that effects the coupling of allylic carbonates such as 6 with aromatic amines to give the secondary amine in high . 

Ellman used silyl chemistry for the direct linkage of aromatics onto the solid support by converting an aryl bromide to aryl lithium and reacting this with a silyl resin.90 It is the production of the silyl resin that is of interest in the context of this review, since an in situ Suzuki coupling was used to link the allyl silane to bromomethyl polystyrene resin (Scheme 40). 9-BBN is used to carry out the regioselective hydroboration, and this is linked to the resin with palladium catalysis in the usual way. After brief exposure of this... 

Five-carbon-atom-chain extensions have been achieved with three kinds of unsaturated compounds 1,4-dienes, 2,4-dienoic acids or esters, and N-2,4-dienylamines. The 1,4-dienes are generally useful with aromatic halides, but give mixtures of isomeric amines with most vinylic halides because of elimination and readdition of palladium hydride in both possible directions to produce two different 7r-allylic intermediates. Exceptions occur in cases where symmetrical compounds are being formed and where both directions of elimination lead to the same product (8). For example ... 

Corey etal. achieved over 90% ee by using their catalyst with KOClat-40°C [33]. Allylic alcohols can be used in the above asymmetric reaction through direct conversion to chiral epoxyketones with aromatic and aliphatic side chains (Scheme 3.13) [34]. 

A direct transformation of functionalized aromatic/heteroaromatic halides into sul-fones has been performed via reactions of organomagnesium intermediates with sulfur dioxide (Scheme 19).98 The ratio of sulfones has been considerably increased by the use of polar aprotic solvents such as DMF or DMSO and of allylic and primary halides. 

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