TBAI‐Catalysed Formal [4+4]‐Cycloaddition: Easy Access to Oxa‐Bridged Eight‐Membered Heterocycles

Abstract

-cyclization reaction of anthranils with hydrazones to deliver oxa-bridged eight-membered heterocycles in accepted yields was developed. Preliminary mechanistic studies indicated that the reaction involved the in situ generation of vinyldiazenes from readily available hydrazones followed by an aza-Michael addition of the anthranil substrates onto the vinyldiazenes and subsequent annulation. This transformation involved the formation of two new CÀ N bonds and CÀ O bond in one pot, overcoming the synthetic limitations of anthranils in organic chemistry. This strategy benefits from high efficiency and atomic economy with mild reaction conditions.

Recent advances in [4 + 4] annulation of conjugated heterodienes with 1,4-dipolar species for the synthesis of eight-membered heterocycles

“…Up to now, the efficient assembly of other types of eight-membered heterocycles (such as triazocines 61 ) using a relevant strategy has been rarely explored. Therefore, more attention needs to be paid to this subject.…”

“…Recently, the Cui and Wu group synthesized fluoroalkyl-substituted oxa-bridged triazocine derivatives using a TBAI-catalyzed formal [4 + 4] cycloaddition. 61 In the presence of TBAI and K 2 S 2 O 8 , a broad spectrum of novel oxa-bridged eight-membered N-heterocycles 130 were prepared in moderate to good yields from the reactions between anthranils 91 and fluoroalkyl-containing hydrazones 129 (Scheme 21). The advantages of the method include atom economy, high efficiency, and mild reaction conditions.…”