Triflate, Bismuth

The carbonyl group can be deprotected by acid-catalyzed hydrolysis by the general mechanism for acetal hydrolysis (see Part A, Section 7.1). A number of Lewis acids have also been used to remove acetal protective groups. Hydrolysis is promoted by LiBF4 in acetonitrile.249 Bismuth triflate promotes hydrolysis of dimethoxy, diethoxy, and dioxolane acetals.250 The dimethyl and diethyl acetals are cleaved by 0.1-1.0 mol % of catalyst in aqueous THF at room temperature, whereas dioxolanes require reflux. Bismuth nitrate also catalyzes acetal hydrolysis.251... 

Scheme 11.4 shows some other representative Friedel-Crafts acylation reactions. Entries 1 and 2 show typical Friedel-Crafts acylation reactions using A1C13. Entries 3 and 4 are similar, but include some functionality in the acylating reagents. Entry 5 involves formation of a mixed trifluoroacetic anhydride, followed by acylation in 85% H3PO4. The reaction was conducted on a kilogram scale and provides a starting material for the synthesis of tamoxifen. Entry 6 illustrates the use of bismuth triflate as... 

Ogawa, C. Azoulay, S. Kobayashi, S. (2005) Bismuth triflate-chiral bipyridine complex catalyzed asymmetric ring opening reactions of meso-epoxide in water., Heterocycles, 66 201-206. 

Discovery of water-compatible Lewis acids has greatly expanded the use of Lewis acids in organic synthesis in aqueous media. However, conventional Lewis acids such as Alm, Tifv, Snfv, etc. still cannot be used in aqueous media under standard conditions. Bismuth triflate, Bi(OTf>3, is reported to exist in water as an equilibrium mixture of Bi(OTf)3 with bismuth hydroxide and triflic acid [18]. 

I2 vapor is extremely corrosive while scandium compounds are moisture-sensitive and very expensive. In addition, these reactions are carried out in an environmentally unfriendly solvent, CH2CI2. We have reported the bismuth triflate-catalyzed synthesis of substituted dihydro-2//-1-benzopyrans by the condensation of substituted salicylaldehydes with 2,2-dimethoxypropane (Scheme 3) [22]. 

We have previously reported that when the rearrangement of trans-stilbene oxide was carried out with CF3SO3H, the solution turned red and the product diphenylacetaldehyde was less pure than that obtained with bismuth triflate. This observation points to the role of bismuth(III) triflate as a Lewis acid in the rearrangement of epoxides and not to protic acid catalysis by triflic acid released by hydrolysis of bismuth triflate. 

We developed a method for the synthesis of a variety of cyclic acetals that utilizes bismuth triflate as a catalyst and does not require the use of a Dean-Stark trap for removal of water [102]. In this method, an aldehyde or ketone is treated with 1,2-bis (trimethylsiloxy)ethane in the presence of bismuth triflate. A comparison study using o-chlorobenzaldehyde showed that with ethylene glycol a low conversion to the dioxolane was observed after 2 h whereas the use of the 1,2-bis(trimethylsiloxy) ethane afforded the corresponding dioxolane in good yields. (Scheme 9). 

Acyclic acetals are simple protecting groups for aldehydes and ketones, and we have previously reported their synthesis catalyzed by Bi(OTf)3 [104]. Acyclic acetals can also be converted to other useful functional groups. For example, allylation of acyclic acetals to give homoallyl ethers has been well investigated, and we have reported a Bi(OTf)3-catalyzed method for the same [105]. The success of Bi(OTf)3-catalyzed formation and allylation of acyclic acetals prompted us to develop a one-pot method for the synthesis of homoallyl ethers from aldehydes, catalyzed by bismuth triflate. A one-pot process saves steps by eliminating the need for isolation of the intermediate and thus minimizes waste. Three one-pot procedures for the synthesis of homoallyl ethers were developed [106]. 

Carrigan MC, Eash KJ, Oswald MC, Mohan RS (2001) An efficient method for the chemoselective synthesis of acylals from aromatic aldehydes using bismuth triflate. Tetrahedron Lett 42 8133-8135... 

Nguyen MP, Arnold JN, Peterson KE, Mohan RS (2004) Environment-friendly organic synthesis using bismuth compounds bismuth triflate catalyzed synthesis of substituted... 

Carrigan MD, Sarapa D, Smith RC, Wieland LC, Mohan RS (2002) A simple and efficient chemoselective method for the catalytic deprotection of acetals and ketals using bismuth triflate. J Org Chem 67 1027-1030... 

Wieland LC, Zerth HM, Mohan RS (2002) Bismuth triflate catalyzed allylation of acetals a simple and mild method for synthesis of homoallyl ethers. Tetrahedron Lett 43 4597 1600... 

Anzalone PW, Baru AR, Danielson EM, Hayes PD, Nguyen MP, Panico AF, Smith RC, Mohan RS (2005) Bismuth compounds in organic synthesis a one-pot synthesis of homoallyl ethers and homoallyl acetates from aldehydes catalyzed by bismuth triflate. J Org Chem 70 2091-2096... 

Keywords Aza-Sakurai allylationreaction Bismuth triflate C-C bond formation Mannich-type reaction Mukaiyama aldol reaction /V-AI koxycaihony I am ino sulfones Silyl nucleophiles... 

Bismuth Triflate-Catalyzed Sakurai Allylation Reaction. 71... 

Bismuth Triflate-Catalyzed Mannich-Type Reaction. 81... 

Initial investigations in the Mannich-type reaction of silyl enolates with benzal-dehyde and aniline employed a series of bismuth(III) salts (Scheme 9, Table 10). These results were promising because the corresponding (l-amino ketone could be obtained in moderate to good yield with bismuth halides, except bismuth fluoride (Table 10, entries 1 1). Bismuth nitrate smoothly afforded the expected product (Table 10, entry 5). While bismuth acetate gave no conversion, bismuth trifluor-oacetate provided the product in only moderate yield (Table 10, entries 6 and 7). Phenyl bismuth ditriflate and diphenyl bismuth triflate appeared to be more efficient catalysts than all those previously tested (Table 10, entries 8 and 9). Bismuth(III) triflate led to the expected product in a good yield and in a short reaction time, without any difference between the anhydrous and the hydrated form (Table 10, entries 10 and 11). 

Bismuth triflate has been reported by Dubac as an efficient catalyst for the Mukaiyama aldol reaction with silyl enol ethers [27] and was recently used with a chiral ligand, as reported by Kobayashi in an elegant hydroxymethylation reaction... 

Keywords Bismuth triflate Bismuth(III) salts Corticosteroids Steroids... 

Various epoxides and aziridines undergo smooth ring opening with water in presence of bismuth triflate (10 mol%) to provide the corresponding v/c-diols and p-amino alcohols with excellent regioselectivity [35]. Reaction of styrene oxide with water in the presence of Bi(OTf)3 affords styrene 1,2-diols (Fig. 7). Similarly,... 

Bismuth triflate catalyzes the synthesis of 1,2-dihydroquinolines in an improved version of Skraup s procedure [74]. Accordingly, treatment of aniline with... 

Tetrahydropyrans hydroxylated at the 4-position have good synthetic value [113]. Although many synthetic methods have been reported [17-23,114,115], the search for potential alternate approaches and the development of eco-friendly and high-yielding reactions resulted in the development of a method that poses less problems for the environment. Synthesis of tetrahydropyranol derivatives can be achieved through the Prins-type cyclization reaction of homoallylic alcohols with aldehydes using bismuth triflate as catalyst in [bmim]PF6 solvent system [108] (Fig. 22). 

OTf)3 (5 mol%). The use of bismuth triflate/[bmim]BF4 is the ideal catalytic system for these condensations because the recovery and reuse of bismuth triflate is especially easy in ionic liquids compared to toluene. 

A variety of methods have been developed for the preparation of substituted benzimidazoles. Of these, one of the most traditional methods involves the condensation of an o-phenylenediamine with carboxylic acid or its derivatives. Subsequently, several improved protocols have been developed for the synthesis of benzimidazoles via the condensation of o-phenylenediamines with aldehydes in the presence of acid catalysts under various reaction conditions. However, many of these methods suffer from certain drawbacks, including longer reaction times, unsatisfactory yields, harsh reaction conditions, expensive reagents, tedious work-up procedures, co-occurrence of several side reactions, and poor selectivity. Bismuth triflate provides a handy alternative to the conventional methods. It catalyzes the reaction of mono- and disubstituted aryl 1,2-diamines with aromatic aldehydes bearing either electron-rich or electron-deficient substituents on the aromatic ring in the presence of Bi(OTf)3 (10 mol%) in water, resulting in the formation of benzimidazole [119] (Fig. 29). Furthermore, the reaction also works well with heteroaromatic aldehydes. 

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