Benzyl alcohol bromide anion

After the nucleophilic attack of the bromide anion on the Sn atoms of the tributylstannyl ether 36 you get oxyanions at C-3 and C-6 as the reactive species. Now selective benzylation can proceed and the alcohol at C-4 is only benzylated as a by-product in low yield. 

Carbonylation with iron carbonyls parallels that of cobalt carbonyls. Benzylic chlorides and bromides are carbonylated with Fe(CO)5 in the presence of base. Esters are realized when carbonylation is performed in alcohols under 1 atm of CO with catalytic amounts of iron pentacarbonyl415. Under phase transfer conditions, two predominant routes are available. With catalytic amounts of iron under a CO atmosphere and strongly basic conditions, the carboxylic acids are realized in reasonable yields415,416, whereas mild bases [Ca(OH)2l, stoichiometric amounts of iron carbonyl and the omission of CO give dibenzyl ketones417. In at least a few cases, it is possible to prepare unsymmetrical methyl benzyl ketones418, des Abbayes and coworkers have observed the formation of acyltetracarbonyl anion (52) under the reaction conditions, and have proposed the catalytic cycle in Scheme 8 for the ketone formation418. 

Many sensitive substrates would not survive the ravages of sodium or potassium hydride and the attendant alkoxide anions. There are gentler methods, An alcohol can be protected with benzyl bromide in the presence of silver I) oxide in... 

Vanhoye and coworkers [402] synthesized aldehydes by using the electrogenerated radical anion of iron pentacarbonyl to reduce iodoethane and benzyl bromide in the presence of carbon monoxide. Esters can be prepared catalytically from alkyl halides and alcohols in the presence of iron pentacarbonyl [403]. Yoshida and coworkers reduced mixtures of organic halides and iron pentacarbonyl and then introduced an electrophile to obtain carbonyl compounds [404] and converted alkyl halides into aldehydes by using iron pentacarbonyl as a catalyst [405,406]. Finally, a review by Torii [407] provides references to additional papers that deal with catalytic processes involving complexes of nickel, cobalt, iron, palladium, rhodium, platinum, chromium, molybdenum, tungsten, manganese, rhenium, tin, lead, zinc, mercury, and titanium. 

Some routes leading to transformation of carbanions into cations were described4585. One of the methods involves capping carbanions with bromine and conversion via Grig-nard into reactive benzyl bromides that could be oxidized by silver salts. Alternatively, phosgene could be used as the reagent4595. Conversion of cations into anions is exemplified by the reaction of living polytetrahydrofuran with lithium salt of cinamyl alcohol,... 

The use of carbon nucleophiles stabilized by SR groups has been a feature of sulphur chemistry for many years now, and this year has seen additional uses for these versatile reagents. Thus the carbanion CH(SPh)2 adds in a 1,2-manner to 2-methylacrolein giving the allyl alcohol (175), which is then converted to the activated diene (176) by standard methodology. The latter has been used in studies towards the total synthesis of the Rubradirin antibiotics. The related anion ArC(SPh)2 also adds to a,/3-unsaturated systems however, in the case of lactone (177) conjugate addition is observed. If the initial ion from (177) is trapped with benzylic bromides then frans-butyrolactones (178) are obtained in good yield. ... 

Preparation.—From Amines or Alcohols. Katritzky has reviewed mechanistic and preparative aspects of the conversion of primary amino to other functional groups mediated by pyrilium cations according to the general Scheme 34, where nucleophiles include the halide anions (cf. 4,157) and carboxylates (c/. 4,138), Other recent publications in this area have included full details of the preparation of primary alkyl and benzyl fluorides by this route using 2,4,6-triphenylpyrilium salts (4,157). The conversion of primary amines to the corresponding bromides has now been improved, either by a modified pyrolysis procedure but still... 

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