Synthesis of Halogenated Cyclic Enamines from Cyclic N‐2‐En‐4‐ynyl‐N‐1‐ynylamides and N‐Propargyl‐N‐1‐ynylamides via a Tandem Iron Halide Promoted N‐to‐C Shift‐Aza‐Prins Cyclization Sequence

Abstract

A facile and efficient N-to-C allyl shiftaza-Prins cyclization sequence of cyclic N-2-en-4ynyl-N-1-ynylamides is promoted by iron(III) chloride, generating chloro-containing bridged bicyclic enamines in minutes and in high yields. This reaction involves an unprecedented formation of a ketenimine via Fe(III)-mediated N-to-C allyl rearrangement, followed by aza-Prins cyclization. This sequence can also be applied to the generation of brominated cyclobutenamine derivatives using Fe(III) bromide and N-propargyl-N-1-ynylamides.

Metal-free [2 + 2] and [4 + 2] cycloadditions ofN-aryl-substituted ynamides to construct functionalized aminocyclobutenes and 4-aminoquinolines

“…3,4 Of particular interest are the aminocyclobutenes. 5 Although many impressive synthetic routes to aminocyclobutenes and 4-aminoquinolines have been explored in the past decades, 6–10 accessing these important structures by convenient and atom-economical methods remains an intriguing objective, especially in synthesizing them under transition-metal-free reaction conditions.…”

“…[2 + 2] Cycloaddition of ynamides 11 with alkene partners represents the most popular route to construct aminocyclobutenes. 6–8 However, its widespread application in the synthesis of aminocyclobutenes is precluded by the frequent use of expensive or environmentally unfriendly metallic salts, which are required to activate ynamides. 6 Up to now, successful examples of the efficient transition-metal-free synthesis of functionalized aminocyclobutenes from ynamides or their analogues have been quite scarce.…”

“…6–8 However, its widespread application in the synthesis of aminocyclobutenes is precluded by the frequent use of expensive or environmentally unfriendly metallic salts, which are required to activate ynamides. 6 Up to now, successful examples of the efficient transition-metal-free synthesis of functionalized aminocyclobutenes from ynamides or their analogues have been quite scarce. 7,8 In 2006, Danheiser and co-workers realized the metal-free approach to aminocyclobutenes through the [2 + 2] cycloaddition of ynamides with ketenes.…”