Efficient Cu-catalyzed intramolecular O-arylation for synthesis of benzoxazoles in water

Rapid and Simple Microwave-Assisted Synthesis of Benzoxazoles Catalyzed by [CholineCl][Oxalic Acid]

Microwave irradiation has been used to enhance the reaction yields and selectivities for organic transformation. In this paper, microwave irradiation (MW) was investigated for the environmentally benign synthesis of benzoxazoles through the cyclization of 2-aminophenols and benzaldehydes using deep eutectic solvent (DES) as a catalyst. The [CholineCl][oxalic acid] was easily synthesized from choline chloride with oxalic acid and used without further purification. [CholineCl][oxalic acid] catalyzed the synthesis of benzoxazoles to produce the desired product in a good to excellent conversion and selectivity under MW irradiation. The presence of [CholineCl][oxalic acid] helps to promote the rapid heating transfer from microwave irradiation into the reaction mixture. The [CholineCl][oxalic acid] can be recovered and reused several times without a considerable degradation in catalytic activity.

Copper(II)-catalyzed synthesis of benzoxazoles from inactive 2-chloroanilides

Aim and Objective:

Benzoxazoles are of great importance in natural products, pharmaceutical agents as well as synthetic intermediates. Although many works reported on construction of benzoxazoles by Cu-catalyzed intramolecular O-arylation of ortho-haloanilides have been improved, there are very few reports about transition metal-catalyzed synthesis of benzoxazoles from inactive 2-chloroanilides so far. This work is to explore a green and cheap protocol for intramolecular O-arylation of inactive 2-chloroanilides to prepare 2-arylbenzoxazoles.

Materials and Methods:

We have found Cu(acac)2/1,10-Phen complex was beneficial to intramolecular O-arylation of 2-chloroanilides using K2CO3 as base in EtOH at 90 oC to prepare benzoxazoles.

Results:

An efficient and green method was developed for Cu(II)-catalyzed intramolecular O-arylation of inactive 2-chloroanilides.

Conclusion:

In this way, many 2-arylbenzoxazoles were prepared in good yields.

A green approach for the synthesis of 2-substituted benzoxazoles and benzothiazoles via coupling/cyclization reactions

We have developed the green method for the synthesis of benzoxazoles and benzothiazoles with moderate to good yields using imidazolium chlorozincate (II) ionic liquid supported into Fe3O4 nanoparticles (LAIL@MNP) under solvent-free sonication. The reaction was performed under mild conditions and only produced water as a sole byproduct. The reactions under solvent-free sonication showed advantages of faster reaction rate (30 min) and high yields of the products (up to 90%). Moreover, the LAIL@MNP material was easily separated from the reaction mixture and can be recycled for five consecutive runs with a slight decrease in its catalytic performance (from 82 to 73%).

Cu(II)/Vasicine Promoted Intramolecular C-O Formation: Synthesis of Benzoxazoles in EtOH

AIMS AND OBJECTIVES

Benzoxazoles are valuable bicyclic aromatic compounds; the construction of benzoxazoles via C-O cross-coupling reactions has attracted more and more attention.

MATERIALS AND METHODS

The best condition of C-O bond formation from o-haloanilides was carried out, taking Cu(OTf)₂ (5 mol%) and vasicine (10 mol%) as the catalysts in EtOH in the presence of K₂CO₃ (2 eq.) for 12 h at 90°C.

RESULTS

A series of 2-substituted benzoxazoles have been prepared in high yields from 2-bromoanilides and 2- iodioanilides under mild conditions.

CONCLUSION

We have developed an efficient Cu-vasicine catalytic system for intramolecular C-O bond formation. This strategy is applicable to the synthesis of a wide variety of 2-substituted benzoxazoles by intramolecular O-arylation of o-haloanilides.