Alkyl bromides are typically more commercially available that the tosylates. Another reason is tosylates usually have higher boiling points, making it easier to raise the reaction temperature. The tosylates are slightly better leaving groups than bromides (more stable anion) making them more reactive.

Generally, both tosylates and bromides should work but the availability and reaction temperature would affect my choice. 

N- alkylation, -acylation and -sulfonation although seeming similar there are not the same reaction. As well pointed before, depends what you want to do with the N‑resulting product. If you want for example increase the nucleophilicity/electron density of you initial substrate or the opposite, or just a good protecting group which you can easily release later. Alkyl groups will be “activators” acyl and sulphonyl will “deactivate” the substrate. Benzyl halides and t-Butoxycarbonyl carbonate (di-tert-butyl dicarbonate) are commonly used since are easily removed afterwards and are good examples of donating and withdrawing electron density groups. For your substrate, the eventual enol form will be slightly increased with alkyls and significantly reduced (when compared with the starting isoindigo) if you introduce a sulfonyl or acyl group.

Good luck

when compared to halo leaving group, tosyl is best leaving group. but you need to prepare the alkyltosylsulfonates, a time consuming process. For N-alkylation, using commercially available alkyl bromides is the best way to prepare your N-alkylated products. Reaction: Potassium carbonate(2.0eq), 2-Butanone, alkyl bromides(1.15eq) and RM(1.0eq)

The most suitable method might also depend on the nucleophilicity/reactivity of your amine. Can you be slightly more specific on the structure of your compound? If I search on isoindigo I only find a general structure which does not contain amines.

The problem with amines is that the alkylated amine is MORE REACTIVE than the original one, so it is impossible to control such reaction.

For instance, if one reacts ammonia with an alkyl halide, a quaternary ammonium halide will be obtain as a major product.

The difficult task is to obtain the primary amine. Methods like Gabriel synthesis deal with that problem.

Alkyl p-toluenesulfonate be used to alkylate the amine group present in any organic compounds as sulphonate group is better leaving group.

Many thanks.

@Carim van Beek

the compound is 6,6'-dibromoisoindigo

Dear Shu Er Tan 

In indigo, isoindigo, Carbazole, indole, and other N-containing heterocycles the pair of electrons of Nitrogen will be delocalized (in a more or less extent, depending on the aromaticity, or pattern of substitution of the particular ring). Likewise the nitrogen will be poor or a very poor nucleophile (for example indole will be preferentially alkylated at C-3 and not at N-1; pyrrole for example will react with electrophiles at C-2 and not N-1). Generally, sulfonyl halides are much better electrophiles than acyl halides and these better than alkyl halides. If you have a very powerful electrophile you will have better chances of a cleaner and more efficient reaction (N-derivatization in your case). For example, toluene will be sulfonated by reaction with a chlorosulfonic derivative, but it will not be alkylate by an alkyl halide unless you add previously a catalyst such AlCl3). if you reflux carbazole with acetic anhydride you will get the N-acetyl derivative – not very cleanly, but you will ) but instead if you use an alkyl halide the reaction will be very difficult to occur – in this case you must form the carbazole anion with Sodium or potassium metal or other very strong base and only then add the halide).

One pot reaction is most of the times preferable, and as I pointed before, depends greatly how you will be using next your alkyl, acyl or sulfonyl product, and the "modulation" of the electron density at the ring.

Regards,

Hi Shu Er Tan,

Please correct me if I'm wrong, however when I search isoindigo structures, I only find amide functionalities (nitrogen directly attached to the carbonyl), not amine. If that is the case, you're looking at a completely different type of reaction in terms of alkylation, as it's an amide you wish to alkylate, not an amine. An amide nitrogen contains a very different electronic configuration/reactivity. For amide alkylation, here are some possible reactions:

http://www.organic-chemistry.org/synthesis/C1N/amides2.shtm

Again, if I misunderstood, my apologies.

Regards,

Hi Carim van Beek,

I am so sorry. I just noticed that I have wrongly typed the question. Ya, that's the amide groups in the isoindigo, not amine. 

Many thanks.