Benzyl triflate

Ethyl triflate and benzyl triflate react with the cubane at room temperature and yield phosphonium salts. Upon protonation even di- and trications could be observed [88,89]. 

Benzyl ethers.2 Benzyl ethers of sugar alcohols can be obtained in 82-98% isolated yield by reaction with 1 and catalytic amounts of triflic acid under these conditions isopropylidene and benzylidene acetal groups are stable, as well as ester and imide groups. The reagent thus is comparable to benzyl triflate (6,44). 

The solvolyses in aqueous dioxan of the benzyl triflates (257 X = O-triflate Y = H) have been studied to examine the effect of conformation on phenyl assistance to ionization. The exo-isomer (257 X = O-triflate, Y = H) solvolyses much faster than the endo-isomer (257 X = H, Y = O-triflate) due to -participation of the face benzene ring. Details of the preparation and characterization of the alcohols (257 X = OH,Y = H) and (257 X = H, Y = OH) have been reported. ... 

Phase-transfer catalysts e.g. benzyltriethylammonium chloride and tetrabutyl-ammonium bromide) have been used in the preparation of O-methyl and 0-benzyl ethers and acetals of formaldehyde e.g. methyl 4,6-O-benzylidene-2,3-0-methylene-a-D-mannopyranoside). A new cyclic ether, methyl 4,6-0-benzylidene-2,3-0-ethylene-a-D-glucopyranoside, resulted when methyl 4,6-0-benzylidene-a-D-glucopyranoside reacted with 1,2-dichloroethane under basic aqueous conditions in the presence of a phase-transfer catalyst. Partially protected sugars e.g. l,2 5,6-di-0-isopropylidene-a-D-gIucofuranose) have also been methylated and benzylated by reaction with methyl and benzyl trifluoro-methanesulphonate (triflate), respectively, using 2,6-di-t-butylpyridine as base. The reactions with benzyl triflate, prepared in situ from benzyl alcohol and trifluoromethanesulphonic anhydride, occurred readily at ca. — 70 °C, whereas those with methyl triflate were performed in refluxing dichloromethane. 

Aldehydes can also be prepared by the carbonylation of aryl and alkenyl halides and triflate, and benzyl and allyl chlorides using tin hydride as a hydride source and Pd(PhjP)4 as a catalyst[377]. Hydrosilancs arc used as another hydride source[378]. The arenediazonium tetralluoroborate 515 is converted into a benzaldehyde derivative rapidly in a good yield by using Et ,SiH or PH MS as the hydride source[379]. 

Benzyl and allyl alcohols which can generate stabilized caibocations give Friedel-Crafts alkylation products with mild Lewis acid catalysts such as scandium triflate. ... 

Lanthanide triflates catalyze the Diels-Alder reaction of imines, generated from anilines and aldehydes, with both dienes and alkenes [26]. Thus N-benzyl-ideneaniline in the presence of Yb(OTf)3 (Scheme 6.16) reacts in organic solvent with open-chain dienes, such as Danishefsky s diene, to give tetrahy-dropyridine derivatives, while with cyclopentadiene and vinylethers and vinylthioethers it works like azadiene in both organic solvent and aqueous medium, affording tetrahydroquinoline derivatives. 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

The related planar pyrrole analog 118 has also been prepared (2) from either ethyl or benzyl pyrrole-2-carboxylate 116. Direct alkylation with diethyl phosphonomethyl triflate (70) and base produced the N-phosphonomethylpyrrole 2-carboxylate 117, which was deprotected with trimethylsilyl bromide and saponified to the corresponding phosphonic acid 118. 

Preparation of 2-fluorofuranoses is also important in relation to the synthesis of biologically active 2 -fluoro derivatives of nucleosides (see Section 111,4). Su and coworkers prepared the 2-triflates 236 and 239 through acid-catalyzed methanolysis of 3,5-di-O-benzyl-1,2-(9-isopropylidene-a-D-ribofuranose [to give 235 (major) and 238] and subsequent triflylation. On treatment with fluoride ion, the anomer 236 afforded exclusively the furan derivative 237, whereas the a anomer 239 gave the 2-fluoro compound 240... 

The 4-triflates 277, 279, and 281 of benzyl 2,3-anhydro-o -D- and -) -L-ri-bopyranosides and -a-D-lyxopyranoside gave, - readily, on reaction with BU4NF [CgHg (24 h) or MeCN (5-8 h), r.t.], the respective 2,3-anhydro-4-deoxy-4-fluoro derivatives 278,280, and 282 in good yields. The conformation ( //s) of the starting compounds remained the same after fluorination. Methyl 2,3-anhydro-4-deoxy-4-fluoro-a-L-lyxopyranoside (284, 86%) was prepared from the 4-triflate 283 by treatment with EtjN- 3HF (CH2CI2-EtjN, 40°, 5 h). 

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