To develop a new facile protocol for the synthesis of 2′-aminobenzothiazolo-arylmethyl-2-naphthol derivatives, N-bromosuccinimide (NBS) was used as an efficient catalyst for the one-pot synthesis of 2′-aminobenzothiazolo-arylmethyl-2-naphthols in excellent yields from
Organic reactions under solvent-free conditions have attracted much interest of chemists particularly from the viewpoint of green chemistry. Green chemistry approaches are significant due to the reduction in byproducts, reduction in produced waste, and reduction of energy cost. The possibility of performing multicomponent reactions under solvent-free conditions with a heterogeneous catalyst could enhance their efficiency from an economic as well as an ecological point of view [
The synthesis of new heterocyclic compounds has always been a subject of great interest due to their wide applicability. Heterocyclic compounds occur very widely in nature and are essential to life. Amongst a large variety of heterocyclic compounds, heterocycles containing benzothiazole moiety are of interest because they show some pharmacological and biological activities. Benzothiazole derivatives were reported to possess anti-inflammatory [
The use of organic molecules as catalysts has become an attractive alternative to traditional metal catalysts. Interest in the field of organocatalysis has increased spectacularly in the last few years as the result of both the novelty of the concept and, more importantly, the fact that the efficiency and selectivity of many organocatalytic reactions meet the standards of established organic reactions [
In continuation of our efforts to explore newer reactions for the synthesis of heterocyclic compounds, we wish to report here a facile and improved protocol for preparation of 2′-aminobenzothiazolo-arylmethyl-2-naphthols from
Initially, we decided to explore the role of our catalyst in water and ethanol-water (1 : 1) as solvent system for the synthesis of 2′-aminobenzothiazolo-phenylmethyl-2-naphthol used as a model compound. With respect to the solvent system, the best results were achieved using water (Table
The synthesis of
Entry | Solvent | NBS |
Temperature |
Time |
Yield |
---|---|---|---|---|---|
1 | Water | 10 | 25 | 90 | 59 |
2 | Water | 10 | 60 | 60 | 88 |
3 | Ethanol-water | 10 | 25 | 60 | 56 |
4 | Ethanol-water | 10 | 60 | 30 | 85 |
5 | Neat | 0 | 60 | 60 | 0 |
6 | Neat | 2 | 60 | 30 | 73 |
7 | Neat | 5 | 60 | 20 | 89 |
8 | Neat | 10 | 25 | 60 | 65 |
9 | Neat | 10 | 60 | 10 | 94 |
10 | Neat | 15 | 60 | 10 | 92 |
11 | Neat | 20 | 60 | 10 | 92 |
These results encouraged us to investigate the scope and generality of this new protocol for various aromatic aldehydes under optimized conditions. As shown in Table
Preparation of
Entry | Ar | Time |
Products | Yield |
m.p. |
---|---|---|---|---|---|
1 | C6H5 | 10 |
|
94 | 202–204 |
2 | 4-Cl-C6H4 | 8 |
|
95 | 209-210 |
3 | 4-Me-C6H4 | 10 |
|
92 | 183-184 |
4 | 4-F-C6H4 | 10 |
|
98 | 189-190 |
5 | 4-NO2-C6H4 | 5 |
|
97 | 188-189 |
6 | 4-MeO-C6H4 | 10 |
|
90 | 172-173 |
7 | 3-NO2-C6H4 | 8 |
|
93 | 197–199 |
8 | 2-Cl-C6H4 | 8 |
|
91 | 185-186 |
9 | 2,4-Cl2-C6H4 | 8 |
|
96 | 203-204 |
10 | 4-OH-3-MeO-C6H3 | 15 |
|
88 | 192–194 |
11 | 3,4,5-MeO3C6H2 | 15 |
|
92 | 159-160 |
It is likely that the reagent releases Br+
In summary, we have developed a new facile protocol for the synthesis of 2′-aminobenzothiazolo-arylmethyl-2-naphthol derivatives from the reaction of
A mixture of the
2′
2′
This research program was supported by Foundation of He’nan Educational Committee, China (no: 12B350005).