2,2’- bis / triflate

Triflates of phenols are carbonylated to form aromatic esters by using PhjP[328]. The reaction is 500 times faster if dppp is used[329]. This reaction is a good preparative method for benzoates from phenols and naphthoates (473) from naphthols. Carbonylation of the bis-triflate of axially chiral 1,1 -binaphthyl-2,2 -diol (474) using dppp was claimed to give the monocarboxy-late 475(330]. However, the optically pure dicarboxylate 476 is obtained under similar conditions[331]. The use of 4.4 equiv. of a hindered amine (ethyldiisopropylamine) is crucial for the dicarbonylation. The use of more or less than 4.4 equiv. of the amine gives the monoester 475. 

Mukaiyama aldol reactions have been reported, usually using chiral additives although chiral auxiliaries have also been used. This reaction can also be run with the aldehyde or ketone in the form of its acetal R R C(OR )2> in which case the product is the ether R COCHR2CR R OR instead of 27. Enol acetates and enol ethers also give this product when treated with acetals and TiCLi or a similar catalyst. When the catalyst is dibutyltin bis(triflate), Bu2Sn(OTf)2, aldehydes react, but not their acetals, while acetals of ketones react, but not the ketones themselves. 

Collins and co-workers have also reported on an enantioselective catalytic Diels—Alder cycloaddition, in which zirconocene and titanocene bis(triflate) complexes were used as catalysts [104], The influence of the solvent polarity on the observed levels of stereoselectivity is noteworthy. For example, as shown in Scheme 6.34, with 108 as the catalyst, whereas in CH2C12 (1 mol% catalyst) the endo product was formed with 30% ee (30 1 endoxxo, 88% yield), in CH3N02 solution (5 mol% catalyst) the enantioselectivity was increased to 89% (7 1 endoxxo, 85% yield). Extensive 1H and 19F NMR studies further indicated that a mixture of metallocene—dienophile complexes was present in both solutions (-6 1 in CH2C12 and -2 1 in CH3N02, as shown in Scheme 6.34), and that most probably it was the minor complex isomer that was more reactive and led to the observed major enantiomer. For example, whereas nOe experiments led to ca. 5 % enhancement of the CpH proton signals of the same ring when Hb in the minor complex was irradiated, no enhancements were observed upon irradiation of Ha in the major complex. 

Many chiral, enantiomerically pure zirconocenes are known [20], In order to induce an asymmetric reaction, chiral zirconocenes have to be prepared, of which the most common are [(EBTHI)ZrCl2] EBTHI = r 10-ethylene-l,2-bis(tetrahydroindenyl), see Scheme 8.47 for the corresponding bis(triflate) and Erker s [(NMI)2ZrCl2] (NMI = r 5-neomenthyhn-dene) [21] (see Scheme 8.37). The [(EBTHI)ZrCl2] complex is commercially available as a racemate or in enantiomerically pure form (for a resolution procedure, see the supplementary material of [22]), and the precursor [(EBI)ZrCl2] is available as a racemate. 

Lewis adds based on zirconocene have been employed as catalysts in several reactions. The metallic species used have mainly been the bis(triflate) and the Cp2ZrCl2/AgC104 reagent. 

Asymmetric Diels—Alder catalysis was more successful with dication-like versions of the Zr-EBTHI system, and using conformationally better defined acyl-oxazoline dieno-philes. The bis(triflate) [Zr(EBTHI)(OTf)2] (Scheme 8.47) induced high levels of ee (>90%) in the cycloaddition to cyclopentadiene at low temperatures, especially in the polar solvent 2-nitropropane [87]. 

The isomerization of an O-silyl ketene acetal to a C-silyl ester is catalyzed by a cationic zirconocene—alkoxide complex [92], This catalysis was observed as a side reaction in the zirconocene-catalyzed Mukaiyama aldol reactions and has not yet found synthetic use. The solvent-free bis(triflate) [Cp2Zr(OTf)2] also catalyzes the reaction in nitromethane (no reaction in dichloromethane), but in this case there may be competitive catalysis by TMSOTf (cf. the above discussion of the catalysis of the Mukaiyama aldol reaction) [91] (Scheme 8.51). 

Sato, K. Yoshitomo, A., A Novel Method for Constractions of Beta-D-Maimosidic, 2-Acetamido-2-Deoxy-Beta-D-Mannosidic, and 2-Deoxy-Beta-D-Arabina-Hexopyranosidic Units from the Bis(Triflate) Derivative of Beta-D-Galactoside. Chem. Lett. 1995, 39-40. 

While 10 and 11 remain the most widely used Schrock catalysts, the range of such initiators has been expanded by reaction of the bis(triflate) precursor Mo(OTf)2(=NAr)(=CHR)(DME) (Ar = Ar Ar ) with chiral aryloxide... 

Larry Overman also used (J. Am. Chem. Soc. 2004,126, 14043) a chiral pool starting material, but in a different way. The prochiral enolate 12 showed substantial diastereoselectivity in its reaction with the bis-triflate 13, almost 10 1. Through the power of algebra, it followed that the three diastereomers of 14 were formed in a ratio of 90 9 1. The crystalline 14 was easily isolated in diastereomerically-pure form, and carried on to phenserine 15. This is a new method for the stereocontrolled construction of chiral quaternary centers. 

More recently, a bis(triflate) route has been used by Lindner and Wassing54 to prepare metallacyclopentanes of rhenium. Similar to the report by Yang and Bergman52 this route exploits the acidity of the hydride CpRe(CO)2H2, but instead of... 

At present, the most convenient way for the preparation of 1,3-disubstituted azetidines involves the alkylation of a primary amine with the bis-triflate of a 2-substituted 1,3-propanediol species in the presence of diisopropylethyl-amine <2006JOC7885>. 

Zefirov s reagent reacted similarly affording cw-bis triflates (see Section 12.2.2). The reaction of HTI and alkenes in the presence of salts with nucleofugal anions, such as lithium perchlorate, led to the addition of these anions to the double bond [3]. 

In 2004 an indium-NHC complex was reported which was prepared from an air stable imidazolium salt precursor.29 Reaction of one equivalent of imidazolium salt with InMe3 affords (NHC)InMe2Cl 18 (Scheme 12). The indium-NHC bond distance of 2.267(2) A is shorter than that of InH3(NHC), though longer than the bis-NHC InBr3(NHC)2. Mono-triflate (19) and bis-triflate (20) complexes can also be prepared by treatment of 18 with trimethyl silyl triflate and treatment of 19 with triflic acid respectively. 

Ten-membered. V,.V, ., -tris(tosyl)-l,4,7-triazacyclodecane 31 was obtained by Richman-Atkins reactions of fully tosylated iV,iV -bis(ethanol-2-yl)-l,3-diaminopropane with tosylamide in nearly quantitative yield (Scheme 1) <2001EJ04233>. Interestingly, reaction with benzylamine afforded the analogous macrocyclic product 32 in much lower yield (25%) <2001EJ04233>. Similar 10-membered triazamacrocycle 33 was obtained by the cyclization with propyleneglycol bis(triflate) in 33% yield (Scheme 1) <1999TL7687>. 

Diphosphoniatricyclo[4.4.4.0]tetradecane bis-triflate 302 was obtained by the reaction of l,5-bis(trifluorometha-nesulfonyloxy)pentane with l,6-diphosphabicyclo[4.4.0]decane 179 in 35% yield in a polar solvent, for example, MeCN. Tricyclic [4.4.4.0]tetradecane 302 was reacted with different nucleophiles to give corresponding bridgeheaded biphosphines 304-308. 

The bis(triflates) can be employed as crude materials immediately after their preparation from aldehydes. The advantages of this method are the easy handling of the fluorinating agent and the mild reaction conditions. Other fluorinating agents, such as tetrabutylammonium fluoride or cesium fluoride/18-crown-6. cleave the S —O bonds of the bis(triflates) and thus produce the starting aldehyde. A variation of this method allows the synthesis of 1-fluoro-l-haloalkanes (see Section 1.1.5.4.). ... 

Bu4N(PhjSnF2) (3.7 g. 6 mmol) was added, at rt, to a. solution of the gem-bis(triflatc) (2 mmol) in anhyd CHjClj (25 mL). After stirring for 2 h [8 h in the case of a-branched gem-bis(triflates), pentane (50 mL) was slowly added to the mixture. After separation of the inorganic salts, the solvent was distilled using a 20-cm Vigreux column. The gem-dilluoride was puritied by chromatography (silica gel, pentane). 

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