Alkylation triflate complex

Benzyne, which is generated in situ from 2-(trimethylsilyl)phenyl triflate and KF, acts as an alkyne congener in distannation in the presence of palladium-/ r/-alkyl isocyanide complex.157 A variety of substituted benzyne derivatives inserts into the Sn-Sn bond to give l,2-bis(stannyl)benzenes (Equation (59)). The reaction fails to occur in the presence of other palladium catalysts such as Pd(PPh3)4. 

Much work in the review period has concerned enantioselective substitution in five-membered heterocyclics. The enantioselective alkylation of some pyrroles by unsaturated 2-acylimidazoles catalysed by the bis(oxazolinyl)pyridine-scandium(in) triflate complex (31) has been reported.39 Compound (33) is formed in 98% yield and 94% ee from the 2-acylimidazole (32) and pyrrole at —40 °C. A series of enantiomer- ically pure aziridin-2-ylmethanols has been tested as catalysts in the alkylation of /V-mclhylpyrrolc and (V-methylindole by ,/l-unsalura(cd aldehydes.40 Enantiomeric excesses of up to 75% were observed for the alkylation of /V-mcthylpyrrole by ( >crotonaldehyde using (2.S ,3.S )-3-mclhylazirin-2-yl(diphenyl)methanol TFA salt as catalyst to form (34). 

Methyl trifluoropyruvate alkylates a series of substituted indoles catalysed by the chiral non-racemic 2,2/-bipyridylcopper(II) triflate complex (32) to form methyl 3,3,3- trifluoro-2-hydroxy-2-indole-3-yl propanoates [e.g. (33)] in high enantiomeric excess and good yield.37... 

Enantioselective additions of a,f)-unsaturated 2-acyl imidazoles, catalyzed by bis(oxazolinyl)pyridine-scandium(III)triflate complex, were used for the asymmetric synthesis of 3-substituted indoles. The complex 114 was one of the most promising catalysts. The choice of acetonitrile as the solvent and the use of 4 A molecular sieves were also found to be advantageous. The 2-acyl imidazole residue in the alkylation products of u,(i-unsaturated 2-acyl imidazoles could be transformed into synthetically useful amides, esters, carboxylic acid, ketones, and aldehydes (Scheme 32) [105]. Moreover, the catalyst 114 produced both the intramolecular indole alkylation and the 2-substituted indoles in good yield and enantioselectivity (Scheme 33) [106]. The complex... 

Chiral 2-(3-oxoalkyl)pyrroles and 3-(3-oxoalkyl)indoles can also be accessed by reaction in the presence of 10 mol% of chiral bis(oxazoline)/metal complexes in CH2C12 in very high yields and with ee values over 90% <2005JA4154>. Alkylation of pyrrole and of substituted indoles with, -unsaturated acyl phosphonates <2003JA10780> or 2-acyl N-methylimidazoles catalyzed by a chiral bis(oxazolinyl)pyridine (pybox)/scandium(III) triflate complex also exhibits good enantioselectivity over a broad range of substrates <2005JA8942>. 

The preparation of alkoxy(l-alkynyl)carbene complexes (e.g., of compounds L M = C(OR1)—C=CR) mostly follows the two-step Fischer procedure,14 involving addition of a 1-lithio alkyne LiC=CR to a metal carbonyl L M(CO) to give a metal acylate L M=C(CTLi+) — C= CR14, which is subsequently alkylated with an oxonium salt [R130]BF4,15 an alkyl triflate R10S02C — CF3,16,22 or an alkyl fluorosulfonate R103SF16a,n ... 

The Friedel-Crafts alkylation of the parent pyrrole and of substituted indoles with a,P-unsaturated acyl phospho-nates 468 <2003JA10780> and 2-acyl iV-methylimidazoles 469 catalyzed by the chiral bis(oxazolinyl)pyridine (pybox)/scandium(lIl) triflate complex 467 exhibits good enantioselectivities over a broad range of substrates (Scheme 97, Equation 113) <2005JA8942>. The desired alkylation products 470-472 were formed in good yields and enantioselectivities. 

The anions generated from tetracaibonyl(phosphine) carbene complexes are more reactive in their reactions with organic electrophiles. This is consistent with the observation that the p/iTa of the methyl pentacarbonyl complex (88a) is increased by six orders of magnitude when one of the carbon monoxi ligands is replaced with tributylphosphine. The anion generated fr-om (106) will give good yields of alkylated products with simple alkyl halides such as ethyl bromide however, dialkylation is still a serious side reaction. It has been reported that both pentacarbonyl and tetracarbonyl(phosphine) complexes can be efficiently monoalkylated with alkyl triflates (primary and secondary). The anion (89) for example, can be monoalkyated with the 3-butenyl triflate in 80% yield. ... 

The 177-1,2-azaphospholes are colorless to yellow solids or oils and are stable at ambient temperature <20008417, 1998ICA(270)273, 2003ZNB44>. Most of the reactions reported so far involve the dicoordinated phosphorus atom, which represents the reactive center of the molecule. l,3-Di(fet/-butyl)-5-phenyl-177-l,2-diazaphosphole reacts under mild conditions with alkyl triflates CF38O3R (R = Me, Et) to afford the P-alkylated 1,2-azaphospholium compounds la and lb in quantitative yields. With an equimolar amount of iron nonacarbonyl, the Tj -complex 2 was selectively formed in 63% yield (Scheme 1) <2002EJ01664>. 

However, a most significant observation is in the comparison between the two phase diagrams where it is seen that the smectic phases present in the triflate complexes are retained with dodecylsulphate as the anion. This is unusual if the alkylsulphate is considered as a lateral alkyl chain, where it would normally be the case that smectic phases were suppressed. Further, the phase diagram of the dodecylsulphate complexes shows, for seven homologues, a cubic phase between the Sc and Sa phase. Both of these points deserve comment. 

In some cases the second step does not take place, and the counterion never binds to the metal. This makes the reaction an electrophilic addition, rather than an oxidative addition to the metal, although the latter term is sometimes seen in the literature to describe this type of reaction. An example is the reaction of the highly nucleophilic Co(I) anion, cobaloxime, with an alkyl triflate, a reaction known to go with inversion. Protonation of metal complexes to give metal hydrides is also very common (Eqs. 3.30-3.31). 

Enantioselective Friedel-Crafts alkylation reactions were performed between substituted indoles and methyl trifluoropyruvate, using a chiral nonracemic ( -symmetric 2,2 -bipyridyl copper triflate complex as catalyst. The active copper(II) catalyst was... 

Enantioselective Friedel-Crafts alkylation of indoles with a,P-unsaturated acyl phosphonates was investigated in the presence of bis(oxazolinyl)pyridine-scandium triflate complexes [151]. The intermediate -indolyl acyl phosphonates were converted to the corresponding methyl esters by direct addition of methanol and DBU (1,8-diazobicyclo [5.4.0] undec-7-ene) to the reaction mixture. Various acyl phosphonates and indole derivatives gave the alkylated products in moderate to good yields with high to excellent enantioselectivities (Scheme 12.57). It was also shown that the reaction was quenched by morpholine to give the corresponding amide, and that electron-rich 3-dimethylaminoanisole was also an effective nucleophile in this reaction. 

The described apparent 1,2-shift is not limited to alkyl groups. Thus, when the hydrido triflate complex (51) was reacted with carbon monoxide in CDCI3, quantita-tiveformationofthecorresponding(PCP)Rh(I)complex(52)tookplace(Scheme2.26). This complex has been described as having only a small contribution of the arenium form due to a very strong agostic interaction between the ipso C—H bond and the metal center. 

Cationic (carbene)iron complexes are obtained by alkylation of acyliron complexes with alkylating reagents such as alkyl triflates or Meerwein s salt (Scheme 4-52). " ... 

An optically pure chiral alkene-Fp complex is formed by reaction of the (Z)-2-butene-Fp complex with (/ ,R)-2,3-butanediol. Nucleophiles are added to this complex in a complete stereoselective way. Ring opening of the cyclic alkyl-Fp complexes with trimethylsilyl triflate leads to substituted vinyl ether-Fp complexes as pure enantiomers. The configurational stability of those complexes is limited, however, which requires immediate demetalation to the organic products (Scheme 4-75). ... 

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