Friedel-Crafts reaction, acylation unsaturated acids

A chiral Sc-pybox catalyst from Sc(OTf)3 catalyzes a highly enantioselective Michael-type indole Friedel-Crafts reactions with a variety of )3-substitnfed a, -unsaturated acyl phosphonates and -substituted a,j8-unsaturated 2-acyl imidazoles (Scheme 2). The acyl phosphonate products were efficiently ttansformed into the corresponding esters and amides, whereas the acyl imidazole prodncts were converted to more diverse functionalities snch as esters, amides, carboxyhc acids, ketones, and aldehydes. A nuld and efficient cleavage protocol for the diversification of the 2-acyl imidazole prodncts ntihzing methylating conditions was also developed. 

Acyl-transfer reactions are some of the most important conversions in organic chemistry and biochemistry. Recent work has shown that adjacent cationic groups can also activate amides in acyl-transfer reactions. Friedel-Crafts acylations are known to proceed well with carboxylic acids, acid chlorides (and other halides), and acid anhydrides, but there are virtually no examples of acylations with simple amides.19 During studies related to unsaturated amides, we observed a cyclization reaction that is essentially an intramolecular acyl-transfer reaction involving an amide (eq 15). The indanone product is formed by a cyclization involving the dicationic species (40). To examine this further, the related amides 41 and 42 were studied in superacid promoted conversions (eqs 16-17). It was found that amide 42 leads to the indanone product while 41... 

By in situ MAS NMR spectroscopy, the Koch reaction was also observed upon co-adsorption of butyl alcohols (tert-butyl, isobutyl, and -butyl) and carbon monoxide or of olefins (Ao-butylene and 1-octene), carbon monoxide, and water on HZSM-5 (Ksi/ Ai — 49) under mild conditions (87,88). Under the same conditions, but in the absence of water (89), it was shown that ethylene, isobutylene, and 1-octene undergo the Friedel-Crafts acylation (90) to form unsaturated ketones and stable cyclic five-membered ring carboxonium ions instead of carboxylic acids. Carbonylation of benzene by the direct reaction of benzene and carbon monoxide on solid catalysts was reported by Clingenpeel et al. (91,92). By C MAS NMR spectroscopy, the formation of benzoic acid (178 ppm) and benzaldehyde (206 ppm) was observed on zeolite HY (91), AlC -doped HY (91), and sulfated zirconia (SZA) (92). 

Acyclic a,/3-unsaturated acid chlorides do not undergo this acylation. However, cyclic vinylsilanes also undergo Friedel-Crafts acylation with a,/S-unsaturated acid chlorides to give dienones of type a, which are cyciized by SnCl to cyclopentenones. A typical example is formulated for the reaction of 5-methyl-l-tri-methylsilylcyclopentene (3) with j3,iS-dimethylacryloyl chloride. The first step is conducted with AICI3 and gives 4, which after isolation is cyciized with SnCU to a mixture of 5 and 6. The cyclopentenone 6 is obtained in 55% overall yield after isomerization with RhCU. 

Friedel-Crafts acylation of alkenes (Daizens-Nenitzescu reaction ) with unsaturated acylium ions generated from acid halides and Lewis acids constitutes a general synthesis of divinyl ketones. 

The value of the metal complexation results from control of the reaction, rather than any activation, Lewis acids being excellent catalysts for diene polymerization. Friedel-Crafts acylations of diene complexes have been used for the preparation of dienes, with decomplexation following carbonyl reduc-tion. 5 Decomplexation to afford dienones has been less explored. The intermediate cationic o -complex on treatment with triethyl phosphite or triphenylphosphine affords metal-free. y-unsaturated phospho-nates or phosphonium salts (Scheme 19). The initial s-cis conformation of the diene fragment of the... 

Unsaturated fatty compounds are of interest as renewable raw materials (1). These compounds can be functionalized at the C,C-double bond by electrophilic addition reactions to give new oleochemicals with potentially new and interesting properties. The alkylaluminum chloride-induced Friedel-Crafts acylation of unsaturated fatty compounds (Fig. 1), such as oleic acid [la], 10-undecenoic acid [2a], petroselinic acid [3a], and erucic acid [4a], and the respective esters and alcohols yield the corresponding P,y-unsaturated ketones (2,3). 

The alkylaluminum halide-induced Friedel-Crafts acylation is a very general and synthetically useful reaction that allows the functionalization of unsaturated fatty compounds. Acylations were carried out with different acylating agents such as acyl chlorides, dicarboxylic acid dichlorides, cyclic anhydrides, unsaturated acyl chlorides, and aromatic and heteroaromatic carboxylic acid chlorides, yielding a large... 

In contrast to the aromatic counterpart, very few works have been devoted to the mechanism of the aliphatic Friedel-Crafts acylation. Several mechanisms have been proposed to explain the reaction of 1-methylcyclohexene in acetic acid with zinc chloride catalyst that exclusively gives the 6-acetyl-l-methylcyclohexene. Early discussions by Deno suggest a carbo-cation intermediate. Finally, the observations by Beak of a product isotope effect in the absence of a corresponding kinetic isotope effect in the series of deuterated cyclenes is compelling evidence for a reaction intermediate, such as carbocation species. In the meantime, H.M.R. Hoffmann observed that the acylation of various olefins with acetyl hexachloroantimonate in methylene chloride in the presence of hindered amines affords 8,T-unsaturated ketones. He suggested that the non-conjugated enone is formed via an ene reaction. 

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