The use of BrCCl3-PPh3 in Appel type transformations to esters, O-acyloximes, amides, and acid anhydrides

Abstract

Esters, acyloximes, amides and acid anhydrides have been prepared from the respective carboxylic acids, oximes, amines and alcohols by the use of the reagent combination BrCCl 3 -PPh 3 . The reactions obviate the handling acyl halides or more aggressive reagents PCl 3 , POCl 3 , or SOCl 2 . Furthermore, the environmentally hazardous CCl 4 used in Appel-type reactions is replaced with BrCCl 3 , a reagent of less environmental concern.

Use of Triphenylphosphine-Bromotrichloromethane (PPh3-BrCCl3) in the Preparation of Acylhydrazines, N-Methylamides, Anilides and N-Arylmaleimides From Carboxylic Acids

“…Previously, it had been established that the reactions of the modified Appel reagent BrCCl3-PPh3 are similar to those of CCl4-PPh3. This includes the dehydration of aldoximes and amides to nitriles (1) and the amidation of carboxylic acids (4). Only the actual Appel reaction itself, ie., the transformation of alkanols to haloalkanes with BrCCl3-PPh3 is more complex, where under certain conditions the transfer of the bromo-substituent vs. the chloro-substituent is not selective (2).…”

“…This reaction system is a variation of the Appel reagent [3], where tetrachloromethane (CCl4) is replaced by the environmentally less hazardous BrCCl3. It was noted that the in situ prepared acyl halides could be reacted with alcohols, and primary and secondary amines to esters and amides, respectively [4]. In the following, the treatment of carboxylic acids is followed by their reaction with hydrazines, methylamine and anilines.…”

Our Experience of Using Thermally Recycled Silica Gel in a Teaching and Small Research Laboratory Setting

“…Typical reactions that have been performed and where the reaction mixtures were separated on recycled silica gel are shown in Figures 5-8. They include two Williamson ether syntheses to methyl 4-ethoxybenzoate (3) ( Figure 5) and to the steroidal azobenzene 6 with alkenylazobenzene 7 as side product ( Figure 6) and two reactions that generate triphenylphosphine oxide as a by-product, namely a Wittig reaction to cinnamate 10 ( Figure 7) and a Appel-type reaction utilizing BrCCl3-PPh3 as a reagent [15] to azo cinnamate 13 (Figure 8). For these reactions, the reaction products could be separated by column chromatography on recycled silica gel to give products in yield and purity equal to the products gained from chromatographic separations with commercial (i.e., non-recycled) silica gel.…”

Hydrogenation of Alkenes with NaBH<sub>4</sub>, CH<sub>3</sub>CO<sub>2</sub>H, Pd/C in the Presence of O- and N-Benzyl Functions

“…Methyl ester 14 was prepared by Wittig olefination from 3-benzyloxy-4-methoxybenzaldehyde and methoxycarbonylmethylidenetriphenylphosphorane in a minimal amount of CHCl 3 . Also, N-benzyl amides 27, 29, 31 and 33 were synthesized from the corresponding acids (benzylamine, PPh 3 , BrCCl 3 , CH 2 Cl 2 ) [12]. Substituted dibenzyl ethers 38 and 43 were obtained by Wilkinson-type etherification (ArCH 2 OH, benzyl chloride, KOH, DMSO) as was 2-benzyloxycinnamaldehyde (24) (2-hydroxycinnamaldehyde, benzyl chloride, KOH, DMSO).…”

“…Benzene, toluene and THF were used without prior purification. Benzyl esters 12, 16, 18, 36, and 40 were prepared from the corresponding acids (benzyl alcohol, PPh 3 , BrCCl 3 , CH 2 Cl 2 ) following a known procedure [12]. Methyl ester 14 was prepared by Wittig olefination from 3-benzyloxy-4-methoxybenzaldehyde and methoxycarbonylmethylidenetriphenylphosphorane in a minimal amount of CHCl 3 .…”