Merging [2 + 2] cycloaddition with radical 1,4-Addition: Metal-free access to functionalized cyclobuta[a]naphthalen-4-ols

Feng Liu,¹ Jia-Yin Wang,¹ Peng Zhou, Guigen Li,* Wen-Juan Hao, Shu-Jiang Tu,* Bo Jiang*

(¹These authors contributed equally to this work)

Metal-free [2 + 2] cycloaddition and S-centered radical-induced 1,4-addition cascades have been achieved by treating benzene-linked allene-ynes with aryldiazonium tetrafluoroborates and DABCO-bis(sulfur dioxide) in a one-pot procedure; the reaction provides a greener and more practical access to functionalized cyclobuta[a]naphthalen-4-ols with valuable applications. More than 50 examples are demonstrated with excellent diastereoselectivity and chemical yields. The reaction pathway is proposed to proceed through thefollowing: sequence of [2 + 2] cycloaddition, insertion of SO₂, 1,4-addition, diazotization and tautomerization.

Angew. Chem., Int. Ed. 2017, 56, 15570-15574

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