Direct Metal-Free Entry to Aminocyclobutenes or Aminocyclobutenols from Ynamides: Synthetic Applications

The [2+2] cycloaddition of ynamides with the highly polarized reagent TfC=CHhas been developed to regioselectively afford bis(triflyl)aminocyclobutenes in the absence of catalyst under mild conditions. Incidentally, with the ynamides bearing electron-rich aromatic rings at the C-terminal, an interesting reactivity switch was observed; a cyclization/hydroxylation sequence yielded 2-amino-3-(triflyl)cyclobut-2-enols. Aminocyclobutene construction with addition of alcohols resulted in the formation of aminocyclobutenyl ethers through a cyclization/hydroalkoxylation process. Moreover, the utility of functionalized aminocyclobutenes as precursors for further elaboration was demonstrated with the preparation of α-amino-β,γ-unsaturated ketones and 3-(triflyl)buta-1,3-dien-2-amines through 4 π-electrocyclic ring opening.Financial support from the MINECO and FEDER (Projects CTQ2012-33664-C02-01, CTQ2012-33664-C02-02, CTQ2015- 65060-C2-1-P, and CTQ2015-65060-C2-2-P) is gratefully acknowledged. We thank Prof. H. Yanai for the kind donation of bis(trifluoromethylsulfonyl)methane. We are grateful to Dr. M. R. Torres for X-ray analysis.Peer Reviewe