Trityl fluoroborate

Treatment of the 2H-1 -benzothiopyran 1 with trityl fluoroborate in nitromethane at room temperature gave the corresponding benzothiopyrylium salt in 90% yield as an unstable green solid which reacted smoothly with 2,3-dimethylbuta-1,3-diene at room temperature to give the expected cycloadduct in 94% yield. Addition of the cycloadduct to an ice-cold solution of... 

Another example results from the synthesis of compound (53) which contains the structural elements of a tetrathiafulvalene and of a quinodimethane. Thus treatment of the bis Grignard reagent of (50) with the 1,3-benzodithiolylium perchlorate (51) leads to (52) which is converted into (53) by subsequent treatment with trityl fluoroborate and triethyl-amine <80AG(E)204>. 

The Lewis acid triphenylmethyl fluoroborate (trityl fluoroborate) has been used to effect net hydride abstraction from 1,3-ditelluroles to give 1,3-ditellurolylium ions (Scheme 9) (82TL1531). There is some question as to whether the loss of hydride occurs by a single two-electron process or by two separate one-electron oxidations coupled with a proton loss. 

The first detailed study of a cationic polymerisation of vinyl ethers induced by stable carbenium salts was reported in 1971 by Bawn et Isobutyl vinyl ether was polymerised with trityl and trc ylium hexadiloroantimonates and trityl fluoroborate. From calorimetric measurements of the rate of polymerisation, it was concluded that all the initiator used was consumed roon after mixii and the assumption was made that an equal number of active species was formed in this fast initiation reaction. Propagation rate constants were thus obtained and attributed to the action of free ions. It was als) claimed that no significant termination took place during the polymerisation ce successive monomer additions produced polymerisations having the same propagation rate constant. Later work performed in the same laboratory on other vinyl ethers... 

ConpBng. Japanese chemists have reported the synthesis of 8,8 -biheplafulvenyl (4) from the bromide (1). Treatment of (1) with magnesium in ether produced 1,2-di(3-cycloJicptatrienyl)cthane (2) in 85 % yield. Hydride abstraction with trityl fluoroborate (1,1256 1258 2. 454 this volume) in methylene chloride gave the salt (3). Treatment... 

Improved preparation. Trityl fluoroborate can be prepared conveniently by the reactions of triphenylmethyl chloride with anhydrous tetrafluoroboric acid-dimethyl ether complex in dry benzene ... 

Oxidmion of ketone acetals and ethers. Ketones can be regenerated from the ethylene acetal derivatives by treatment with trityl fluoroborate in dry dichloro-methanc (Nj) at room temperature. Thus the reaction of trityl fluoroborate with cyclohexanone ethylene acetal results in cyclohexanone (80%) and triphenylmethane. The reaction thus involves hydride transfer to the triphenyl carbonium ions. Triethyl-oxonium fluoroborate can also be used but is somewhat less effective than trityl fluoroborate. 

The reaction is useful in the preparation of keto-sugars. Thus the reaction of trityl fluoroborate with the acelonide (4) derived from D-mannitol gives the keto-sugar (5) in 65 % yield. 

Oxidation of benzyl ethers with trityl fluoroborate can be used either to prepare aromatic aldehydes or to cleave benzyl ethers of alcohols. 

Ketone acetals may be oxidized by hydride transfer, using trityl fluoroborate (see also Part II, Chap. 2, p. 388). ° Ethylene acetals of steroidal ketones afforded the parent ketones in good yield, under non-polar conditions (in CH2CI2 at room temperature). The proposed mechanism (Scheme 3) results in oxidation... 

A new cortisone derivative, 3,20-dioxo-lljS,17a,21-trihydroxypregna-l,4,7-triene (298), has been prepared from the intermediate (297) by a classical combination of chemical and microbiological reactions.The chemistry of 17,20-and 20,21-acetonides, epimeric at C(20), has been described. A deprotection of masked steroidal alcohols by hydride transfer has been reported.Several benzyl ethers and bismethylenedioxy-steroids have been prepared and treated with trityl fluoroborate. The results demonstrated that the benzyl hydrogen atoms are sufficiently basic to give a benzyloxonium ion, as shown in the conversion of the 17,20 20,21-bismethylenedioxy-corticoid (299) into its free analogue (302) (see Part II, Chapter 1, refs. 120 and 323). 

Preparation. The reagent (1) is obtained in 92 % yield as a yellow, crystalline solid by the reaction of 1,3-dithiane (2, 182-187 3, 135-136 this volume) with trityl fluoroborate (1, 1256-1258 this volume) in dry methylene chloride (heating at reflux for 30 min., evaporation of solvent under reduced pressure, trituration with cold ether, and drying under vacuum). The reagent can be stored with exclusion of moisture at — 20° for several months without appreciable decomposition. 

Potassium permanganate. Dimethyl sulfide-Chlorine. Dimethyl sulfoxide. Dimethyl sulfoxide-Chlorine. Dimethylsulf-oxide Sulfur trioxide. Dipyridine chro-mium(VI) oxide. Iodine. Iodine-Potassium iodide. Iodine tris(trifluoroacetate). Iodosobenzene diacetate. Isoamyl nitrite. Lead tetraacetate. Manganese dioxide. Mercuric acetate. Mercuric oxide. Osmium tetroxide—Potassium chlorate. Ozone. Periodic acid. Pertrifluoroacetic acid. Potassium ferrate. Potassium ferricyanide. Potassium nitrosodisulfonate. Ruthenium tetroxide. Selenium dioxide. Silver carbonate. Silver carbonate-Celite. Silver nitrate. Silver oxide. Silver(II) oxide. Sodium hypochlorite. Sulfur trioxide. Thalli-um(III) nitrate. Thallium sulfate. Thalli-um(III) trifluoroacetate. Triphenyl phosphite ozonide. Triphenylphosphine dibromide. Trityl fluoroborate. 

Dehydrogenation. Trityl fluoroborate was the most satisfactory reagent found fo the dehydrogenation of (1) to the dibenzosesquifulvalene (2).5a Yields with chlorani and with N B S-triethylamine were 7% and 1 %, respectively. 

Like trityl perchlorate and trityl fluoroborate (1, 1256-1258 2, 454), this salt can be used for hydride abstraction one advantage over the perchlorate salt is that it is not explosive. It has been used for the conversion of cycloheptatriene into tropylium hexachloroantimonate1 and for conversion of 1,5-diketones into pyrylium salts.2... 

---