Dimethylbromomethyleneammonium Bromide

(1; X = Br)

[24774-61-6]  · C3H7Br2N  · Dimethylbromomethyleneammonium Bromide  · (MW 216.91) (2; X = POBr2)

[-]  · C3H7Br3NOP  · Dimethylbromomethyleneammonium Dibromophosphate  · (MW 343.77)

(conversion of primary, secondary, and tertiary aliphatic alcohols,1 including those in sugars and nucleosides,2 into the corresponding bromides; preparation of b-bromovinyl aldehydes,3 and b-bromo-a,b-unsaturated ketones4)

Physical Data: (1) mp 156-158 °C.

Form Supplied in: prepared in situ.

Preparative Methods: reagent (1) can be prepared by dropwise addition of Thionyl Bromide to DMF in a chlorinated solvent; after the addition is complete, the mixture is heated at 40 °C to remove any remaining sulfur dioxide (eq 1).1

An alternative preparation of this reagent from Triphenylphosphine, Bromine, and N,N-Dimethylformamide is claimed to be easier to perform.1 A third route involves passing gaseous Hydrogen Bromide through a solution of Dimethylchloromethyleneammonium Chloride.1,2

Reagent (2) can be prepared by adding Phosphorus(III) Bromide slowly to DMF in chloroform.2 Reagent (2) is more reactive than the bromide salt (1), which has been accounted for by a rapid exchange of the bromide and dibromophosphate anions (eq 2).

Handling, Storage, and Precautions: the reagents are corrosive, air-sensitive, and lachrymatory, and must be treated with caution. Avoid skin contact. Reagents (1) and (2) must be generated prior to the reaction under anhydrous conditions. An explosion of a flask containing a b-bromovinyl aldehyde has been reported.5 Use in a fume hood.

Conversion of Alcohols into Bromides.

Alcohols have been converted into the corresponding bromides in high yields using reagent (1) (eq 3).1 Hydroxy groups of nucleosides are converted into bromides using similar conditions.3 Thus, yields (%) for the following compounds were obtained: R1/R2 = Me(CH2)3CH2/H (89); CyCH2 (82); PrMeCH (83); Et2CH (82).

The reagent derived from DMF-Triphenylphosphine Dibromide converts primary alcohols into bromides, but converts secondary alcohols into formate esters. Where primary and secondary alcohol functions are present, they are respectively converted into bromide and formate (eq 4).4

Reaction with 1,3-Diketones.

Mewshaw5 reported that cyclic 1,3-diketones can be converted into b-bromo-a,b-unsaturated ketones in high yields using reagent (1) (eq 5). The corresponding b-chloro-a,b-unsaturated ketones have been synthesized using dimethylchloromethyleneammonium chloride. Complexes derived from DMF and Phosphorus Oxychloride can give bis(b-chlorovinyl aldehydes) (eq 6).6

Preparation of b-Bromovinyl Aldehydes.

Reagents (1) and (2) react with methyl or methylene ketones to give b-bromovinyl aldehydes (b-BVAs) (eq 7).2,7,8 Steroidal systems containing a ketone function also undergo this reaction.9

b-BVAs have been used as synthetic intermediates. The bromide group is easily displaced7,9,11 and the aldehyde group is readily converted into other functionalities (eqs 8 and 9).7,10-12 b-BVAs have not received the same level of attention as b-chlorovinyl aldehydes,6,10,13 probably owing to the comparative instability of the former compounds.

Related Reagents.

Dimethylchloromethyleneammonium Chloride; N,N-Dimethylformamide; Phosphorus(III) Bromide.

1. (a) Hepburn, D. R.; Hudson, H. R. JCS(P1) 1976, 754; (a) Hepburn, D. R.; Hudson, H. R. CL(L) 1974, 664.
2. Arnold, Z.; Holy, A. CCC 1961, 26, 3059.
3. (a) Dods, R. F.; Roth, J. S. TL 1969, 12, 165; (b) Dods, R. F.; Roth, J. S. JOC 1969, 34, 1627; (c) Paulsen, H.; Heume, M.; Nurnberger, H. Carbohydr. Res. 1990, 200, 127; (d) Petitou, M.; Duchaussoy, P.; Lederman, I.; Choay, J.; Sinay, P. Carbohydr. Res. 1988, 179, 163.
4. Boeckman, R. K., Jr.; Ganem, B. TL 1974, 913.
5. Mewshaw, R. E. TL 1989, 30, 3753.
6. (a) Katritzky, A. R.; Marson, C. M. TL 1985, 4715; (b) Pulst, M.; Hollborn, B.; Weissenfels, M. JPR 1979, 321, 671; (c) Katritzky, A. R.; Marson, C. M. JOC 1987, 52, 2726.
7. Coates, R. M.; Senter, P. A.; Baker, W. R. JOC 1982, 47, 3597.
8. Jutz, C. Adv. Org. Chem. 1976, 9, 225.
9. Schmitt, J.; Panouse, J. J.; Cornu, P.-J.; Pluchet, H.; Hallot, A.; Comoy, P. BSF 1964, 2760.
10. Pulst, M.; Weissenfels, M. ZC 1976, 16, 337.
11. Acheson, R. M.; Lee, G. C. M. JCS(P1) 1987, 2321.
12. Coates, R. M.; Muskopf, J. W.; Senter, P. A. JOC 1985, 50, 3541.
13. Marson, C. M. T 1992, 48, 3659.

Paul R. Giles & Charles M. Marson

University of Sheffield, UK

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