Synthesis of Spiro[benzofuran-2,3′-pyrazol]-3-imines from Aurone-Derived Azadienes and Hydrazonoyl Chlorides via Regio- and Diastereospecific [2+3] Cycloaddition

Abstract

An array of spiro[benzofuran-2,3'-pyrazol]-3-imines with diverse functional groups were readily assembled from aurone-derived azadienes and in-situ generated nitrilimines under mild conditions. The transformation performed in a regio- and diastereoselective fashion, in which a synergetic [2 + 3] cycloaddition pathway was likely involved. This novel methodology has extended the synthetic application of aurone-derived azadienes as a kind of two-atom synthon.

Advances in the Synthesis of Heterocycles with Two and Three Heteroatoms using Hydrazonoyl Halides

“…When azadienes 170 react with nitrilimines generated under mild conditions from hydrazonoyl chlorides 171 , spiro‐linked benzofuran‐pyrazoles 172 are formed ( Scheme 53). The [2+3] cycloaddition reaction occurs regio‐ and diastereoselectively, and the oxygen‐carbon bond of the benzofuran ring is also not opened [114] …”

“…[113] When azadienes 170 react with nitrilimines generated under mild conditions from hydrazonoyl chlorides 171, spiro-linked benzofuran-pyrazoles 172 are formed (Scheme The [2 + 3] cycloaddition reaction occurs regio-and diastereoselectively, and the oxygen-carbon bond of the benzofuran ring is also not opened. [114] There are examples when the heterocyclic fragment of the original dipolarophile is not retained in the cycloaddition product. By carrying out a reaction similar to that described above in the presence of diazobicyclocyclooctane (DABCO) and molecular sieves when heated in dichloroethane, the (3 + 2)cycloaddition/auronic ring opening product was obtained.…”