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.

A 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 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.