Alkylation hydroalkylation

Keywords Bismuth Friedel-Crafts alkylation Green chemistry Hydroalkylation Hydroarylation... 

This first example of a Bi(OTf)3-catalyzed Friedel-Crafts alkylation originated in the following procedures, including benzylations of 2,4-pentanediones or hydroarylation and hydroalkylation reactions. A related procedure was simultaneously developed by Bonrath et al. [39]. The authors utilized Bi(OTf)3 in the synthesis of (all-rac)-a-tocopherol (Vitamin E) [39], Besides rare earth metal triflates, such as Ga(OTf)3, Hf(OTf)3, Sc(OTf)3 and Gd(OTf)3, Bi(OTf)3 was shown to be the most efficient catalyst for the Friedel-Crafts-type reaction between trimethylhydroquinone acetate 10b and isophytols 11a, b. With only 0.02 mol% Bi(OTf)3 (substrate to catalyst ratio 5,000 1) the desired a-tocopherols 12a and 12b were isolated in excellent yields (Scheme 10). 

On the basis of previous results, the Rueping group started to study alkylations with activated alkenes and nucleophiles other than arenes. Recently, Lewis- and Brpnsted-acid-catalyzed hydroalkylation procedures with 1,3-dicarbonyl compounds as nucleophiles have been developed [69, 70]. These reactions primarily utilized Pd... 

This method can be exploited as part of a one-pot hydroalkylation of an internal alkyne. Thus, titanium-catalyzed syn hydrozincation [24], followed by Negishi cross-coupling with an alkyl halide, stereospecifically generates a trisubstituted olefin (Eq. 8). 

Mechanistic smdies of Pd(MeCN)2Cl2-catalysed hydroalkylation reactions of allylic amine derivatives by n-BuZnBr in the presence of Zn(OTf)2, benzoquinone, and DMA suggested a reversible )3-hydride elimination/hydride insertion process leading to the primary Pd-alkyl intermediate, which underwent trans-metalation followed... 

Palladium Pd(II)-catalysed hydroalkylation of Al-protected allylic amines PG(R )N-CH(R )C=CH2 (PG = protecting group) by Bu"ZnBr and other alkylzinc reagents has been reported to afford anti-Markovnikov products PG(R )N-CH(R )CH2CH2-Bu". Mechanistic studies suggest that a reversible jS-hydride elimination/hydride insertion process furnishes the primary Pd-alkyl intermediate, which undergoes transmetallation followed by reductive elimination to form a new sp -sp carbon-carbon bond. ° DFT PBE/3z calculations have been employed to elucidate the solvent effect on hydroxymethoxycarbonylation of cyclohexene catalysed by (Ph3P)2Pd. ... 

Analogously, Co-catalyzed hydroalkylation of Cgg with reactive alkyl bromides in the presence of Mn reductant and H2O at room temperature gave the monoalkylated Cgo (12) in good to high yields (Scheme 34.3). The reaction probably occurs through a reduced Co(0 or I) complex that promotes generation of a radical (K) and the addition to C50 [32]. 

A method for the preparation of alkanes in which alkylazodiphenylmethanols (5) decompose at 35—50 °C to hydroalkylate olefins has now been examined in detail. The yields, which are only moderate, can be improved by the addition of a hydrogen-atom donor (e.g. phenol). Unsymmetrical olefins are hydroalkyl-ated with the regiochemistry expected for a radical mechanism in which the alkyl radical adds first (Scheme 10). 

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