Friedel-Crafts reaction ring-opening

An ingenious synthesis of 1-arylisoindolcs has been developed by Vebor and Lwowski, based upon the reaction of an o-phthalimido-methylbenzophenone (41, R = aryl) with hydrazine (Table IV). The benzophenone is prepared by a Friedel-Crafts reaction with o-phthalimidomethylbenzoyl chloride (40). The mechanism of isoindole formation can be represented sehematically by a sequence involving attack by hydrazine at the imide to give the ring-opened hj drazide (42), followed by cyclization to phthalazine-l,4-dione (44) with displacement of the o-aminomethylbenzophenone (43). Intramolecular condensation of the latter can lead, via the isoindolenine... 

Typically in ring-opening reactions of aziridines, the amine functional group is retained in the product molecule. An example of such a reaction where the amine group has been lost has recently been reported <06TL977>. An intramolecular Friedel-Craft reaction of aziridine 91 leads to the expected product as an intermediate. Under the rather drastic reaction conditions, the sulfonamide is lost leading to formation of the naphthalene ring. 

Unsaturated 5(4H)-oxazolones undergo a Friedel-Crafts reaction with aromatic hydrocarbons in the presence of a Lewis acid. In particular, a 2-aryl-4-benzylidene-5(4H)-oxazolone 598 reacts with o- or p-xylene in the presence of aluminum chloride via ring opening and subsequent dearylation to yield 599 as indicated in Scheme 7.191. ... 

Asymmetric microbial oxidation afforded the (-)-epoxide which has been explored as a building block ring opening reactions with organometallic nucleophiles, and via Friedel-Crafts reactions have been reported. [226,227]. A non-biotransformative approach to this epoxide has also been described [228]. Copper(II)-catalysed oxidative hydrolysis (Eq. 72) affords a lactic acid analogue in high enantiomeric purity [229]. 

A procedure to introduce a C-11 methoxy group into the aryl ring of (26 Scheme 7) also used a Baeyer-Villiger reaction. Ring opening and subsequent Friedel-Crafts ring closure at a free aiyl position afforded the dimethoxypodocarpic acid derivative (27). 

The previously reportedly ring-expansion of phosphole-dichlorocarbene adducts to dihydrophosphorins has now been studied in detail.14.15 Heating the adducts (21) at 135°C for 3 minutes leads to optimum yields of a mixture of isomeric 1,2-dihydrophosphorin 1-oxides (22) and (23). 14 Mercuric-catalysed ring-opening in acetic acid leads to the isomers (24) and (25).1 Both chlorine atoms in (21) may be replaced by phenyl groups in a Friedel-Crafts reaction. 

The ability to open the furan ring by oxidation has also been utilized for synthesis of trialkylacetic acids A 2-furoic ester is first subjected to a Friedel-Crafts reaction with a tertiary alkyl halide, and the 5-alkyl-2-furoic acid obtained from the product by hydrolysis is then oxidized by alkaline permanganate to the trialkylacetic acid 154... 

The thiophene ring can also be opened up, but in a very different way. Reductive removal of the sulfur atom with Raney nickel reduces not only the C—S bonds but also the double bonds in the ring and the four carbons in the ring form a saturated alkyl chain. If the reduction follows two Friedel—Crafts reactions on thiophene the product is a 1,6-diketone instead of the 1,4-diketones from furan. Thiophene is well behaved in Friedel—Crafts acylations, and reaction occurs at the 2- and 5-positions unless these are blocked. 

Table 7 for one example in this series. The same authors further used the strategy in other reactions, namely ring opening reactions of 3,4-dihy-dropyrans by indoles and Friedel Crafts reactions. ... 

This chapter collects miscellaneous enantioselective nickel-catalysed reactions that could not be included in other chapters, such as cyclisation reactions, amination reactions, ring-opening reactions, Friedel-Crafts reactions, allylation reactions of aldehydes, and other reactions. It well demonstrates the remarkably diverse chemical reactivity exhibited by chiral nickel catalysts. 

The area of reactions of phosphate derivatives has been dominated by highly stereoselective reactions in which the latter were used as chiral catalysts or achiral reagents. Among this group of reactions, it is worthy to note several asymmetric reactions ring opening of w 50-aziridinium and episulfonium ions, addition of alcohols to imines, 1,3-dipolar addition of aldehydes, amino esters and dipolarophiles, protonation of silyl enol ethers, epoxidation of a,p-unsaturated aldehydes, aza-ene-type reactions as well as asymmetric versions of named reactions Mannich, Friedel-Crafts, Kabachnik-Fields, aza-Darzens and aza-Henry. 

Shi and coworkers have identified BF3 OEt2 as the best Lewis acid for the formation of the ring-opened product (149) (Equation 89) [91]. Other Lewis acids and Bronsted acids failed to yield any appreciable amount of the desired product in this novel Friedel-Crafts reaction. 

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