Friedel-Crafts reaction ring size

The sumanene-type heterobuckybowls such as trithiasumanene 132 and trisUasumanene 133 have also been prepared. The former was synthesized from a regioisomeric mixture of tris(chloroethenyl)benzotrithiophenes under FVP conditions at 1,0(X) °C [150]. In contrast, trisUasumanene 133 was prepared by threefold sila-Friedel-Crafts reactions [151]. The two heterobuckybowls provide a suitable model for systematically smdying the influences of the ring size on the structure (Table 7). 

Another synthesis of aryl-substituted methylidynetricobalt nonacar-bonyls was developed by Dolby and Robinson (15) who found that chloro-methylidynetricobalt nonacarbonyl alkylate s aromatic compounds in a Friedel-Crafts-type reaction. High product yields were obtained when equimolar amounts of ClCCo3(CO)9 and aluminum chloride and an excess of the arene were stirred at 60°-70°C for 2 hours. When the arene was a solid, the reaction was carried out in dichloromethanc solution. Both ortho and para substitution was encountered, the size of the substituent (s) already present on the benzene ring appearing to determine the position of substitution (Table IV). Noteworthy is that milder temperature conditions affected the position of substitution thus, reaction of chlorobenzene with chloromethylidynetricobalt nonacarbonyl in dichloromethane at 42° gave... 

Friedel Crafts type alkylations of benzene by alkenes involve the initial formation of a lattice associated carbenium ion, formed by protonation of the sorbed olefin. The chemisorbed alkene is covalently bound to the zeolite in the form of an alkoxy group and the carbenium ion formed exists only in the transition state. As would be expected fixjm conventional Friedel Crafts alkylation, the reaction rate over acidic molecular sieves also increases with the degree of substitution of the aromatic ring (tetramethyl > trimethyl > dimethyl > methyl > unsubstituted benzene). The spatial restrictions induced by the pore size and geometry frequently inhibit the formation of large multisubstituted products (see also the section on shape selectivity). 

This chapter summarizes those transannular reactions in medium ring carbocycles which result in carbon-carbon bond formation via alkylation of carbon, in the presence of electrophilic reagents. It is therefore a logical extension of two other chapters in this volume, covering Friedel-Crafts Alkylations (Chapter 1.8), and Polyene Cyclizations (Chapter 1.9). The discussion of these processes is organized according to the size of the cycloalkene from which transannular cyclization is effected. 

We have seen that the intramolecular version of the Friedel-Crafts acylation reaction is wide-ranging and that reaction conditions can normally be devised to allow the synthesis of a large number of different ring sizes. Cyclizations can also be carried out when the aryl residues have widely differing electron densities. The reaction is subject to fewer anomalies than is the case with the inteimolecular version. There have been examples reported where unexpected products have been obtained, but a careful choice of reaction conditions will normally allow these problems to be avoided. To quote just one example, cinna-moyl chloride (the trans isomer) would not be expected to give a cyclized product, and a reaction with toluene using aluminum chloride as the catalyst leads to the expected inteimolecular reaction product. A reaction carried out in benzene solution, however, gave rise to a mixture of 3-phenylindan-l-one and 1,3,3-triphenylpropanone. 

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