ZnCl2-catalyzed [4 + 2] benzannulation of 2-ethynylbenzaldehydes with alkynes: Selective synthesis of naphthalene derivatives

Zn-catalyzed [4 + 2] benzannulation of 2-ethynylbenzaldehydes with alkynes is described for the selective synthesis of naphthalene derivatives. In the presence of ZnCl2, a variety of 2-ethynylbenzaldehydes underwent the [4 + 2] benzannulation reactions with alkynes to selectively afford the corresponding naphthalene derivatives in moderate to good yields.

Graphical abstractA practical and regiospecific protocol for the selective synthesis of naphthalene derivatives is presented by Zn-catalyzed [4 + 2] benzannulation of 2-ethynylbenzaldehydes with alkynes.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights►A new, inexpensive Zn-catalyzed [4 + 2] benzannulation of 2-ethynylbenzaldehydes with alkynes has been developed for the selective synthesis of naphthalene derivatives.► In the presence of ZnCl2, a variety of 2-ethynylbenzaldehydes underwent the [4 + 2] benzannulation reactions with alkynes to selectively afford the corresponding naphthalene derivatives in moderate to good yields.► Compared with the earlier reports, two features were established: (1) This reaction is practical and regiospecific, and (2) this reaction was carried out using inexpensive Lewis acid catalyst under additive-free conditions.