Phenacyl chloride reduction

The chiral reduction of phenacyl chloride (2) was run using either the methyl- or methoxy- oxazaborolidine (3) as the catalyst. After optimization of the reaction... 

Redactiaa of at-luMteUmes Treatment of x-bromoketones with lithium iodide and boron trifluoride in ether or THF at room temperature affords the parent ketone in high yield. The hydrogen was eventually found to originate, presumably as water, in the lithium iodide (Alfa Inorganics, anhydrous ). Only one exception to the reduction was observed, namely a-bromocamphor failed to react. The procedure is also effective for some x-chloroketones (phenacyl chloride, 2-chloropentanone), but fail.s for hindered chloroketones (oi-chloronorbomanone). 

Angelini described the preparation of dihydro- 1,4-benzothiazine and related compounds from analogous esters by a two-stage reduction using tin and HC1 or lithium aluminum hydride.129 It is interesting to compare the reaction of 2-nitrophenol with similar reagents to produce benzooxazine derivatives. 2-Nitrophenol reacts with a-bromoethyl acetate, and the adduct is cyclized with zinc and ammonium chloride to the hydroxamic derivative 85.130 The adduct with phenacyl chloride has been similarly cyclized under a variety of conditions.131,132... 

This group was developed for protection of the 5 -OH group in nucleosides. The derivative is prepared from the corresponding triaiylmethyl chloride, and is cleaved by reductive cleavage (Zn/AcOH) of the phenacyl ether to the p-hydroxyphenyl-diphenylmethyl ether followed by acidic hydrolysis with formic acid. ... 

Alternatively, the thiazolotriazine ring was prepared from l-nitro-2-aminonaphthalene with an isothiocyanate to give naphthylpyrimidine 669, whose reaction with phenacyl bromide gave thiazoline 670. Reduction with stanous chloride and cyclization with (V-bromosuccinimide gave naphthothiazolotriazine 671 (74JIC631) (Scheme 138). 

Dihydro- and 2,3,5,6-tetrahydro-imidazo[2,l -6 ]thiazoles have been prepared in large numbers by condensation of phenacyl bromides with thiazolines followed by acetylation, sodium borohydride reduction, and ring closure with thionyl chloride and acetic anhydride (Scheme 2) <77JMC563, 66JMC545). 

In DMF containing lithium perchlorate, reduction of o -bromopropiophenone at mercury gives l,4-diphenyl-2,3-dimethylbutan-l,4-dione in 65% yield [236]. However, electrolysis of a-bromopropiophenone in the presence of benzoyl chloride affords only l,3-diphenyl-2-methylpropan-l,3-dione. Other studies involving reduction of phenacyl bromides include the electrosynthesis of 4-aryl-2-methylfurans [237] and the regioselective synthesis of enol carbonates [238] semicarbazones of phenacyl bromide can be converted into 3,7-diaryl-2/7-imidazo[2,l-Z>][l,3,4]oxadiazines [239]. Reduction of 1,2-dibenzoyl-chloroethane at mercury in DMF containing lithium perchlorate affords mixtures of phenyl tribenzoyl cyclopentanols and diphenyl dibenzoyl butanediones [240]. 

Cleavage a to a carbonyl group has been exploited in the use of phenacyl protecting groups. The reduction of compounds such as (3) (for their formation, YiaDichloroketene see Trichloroacetyl Chloride) retains the strained four-membered ring, and often gives excellent yields (eq 11). ... 

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