Alcohol asymmetric Friedel-Crafts reaction

Ricci and co-workers introduced a new class of amino- alcohol- based thiourea derivatives, which were easily accessible in a one-step coupling reaction in nearly quanitative yield from the commercially available chiral amino alcohols and 3,5-bis(trifluoromethyl)phenyl isothiocyanate or isocyanate, respectively (Figure 6.45) [307]. The screening of (thio)urea derivatives 137-140 in the enantioselective Friedel-Crafts reaction of indole with trans-P-nitrostyrene at 20 °C in toluene demonstrated (lR,2S)-cis-l-amino-2-indanol-derived thiourea 139 to be the most active catalyst regarding conversion (95% conv./60h) as well as stereoinduction (35% ee), while the canditates 137, 138, and the urea derivative 140 displayed a lower accelerating effect and poorer asymmetric induction (Figure 6.45). The uncatalyzed reference reaction performed under otherwise identical conditions showed 17% conversion in 65 h reaction time. 

Huorous compounds are also potentially useful as additives to promote organic reactions in carbon dioxide. For example, a fluorous alcohol RfCH20H assists asymmetric hydrogenations with non-fluorous ruthenium BINAP catalysts, and a fluorous aryl alkyl ether (C8F17C6H4-P-OC12H25) does so in scandium-triflate-catalyzed aldol and Friedel-Crafts reactions. These additives are presumed to act as solubilizers or emulsifiers to promote contact among the various reaction components. Since they are fluorous, they can be readily recovered from the otherwise organic reaction mixtures for reuse. 

As catalysts Lewis acids such as AICI3, TiCU, SbFs, BF3, ZnCh or FeCl3 are used. Protic acids such as FI2SO4 or FIF are also used, especially for reaction with alkenes or alcohols. Recent developments include the use of acidic polymer resins, e.g. Nafion-Fl, as catalysts for Friedel-Crafts alkylations and the use of asymmetric 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. 

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