<jats:title>Abstract</jats:title><jats:p>Two new cyclobutanoid amides, piperarborenine A (=1,1′‐{[(1<jats:italic>α</jats:italic>,2<jats:italic>α</jats:italic>,3<jats:italic>β</jats:italic>,4<jats:italic>β</jats:italic>)‐2,4‐bis(3,4‐dimethoxyphenyl)cyclobutane‐1,3‐diyl]dicarbonyl}bis[5,6‐dihydropyridin‐2(1<jats:italic>H</jats:italic>)‐one]; <jats:bold>1</jats:bold>) and piperarborenine B (=1,1′‐{[(1<jats:italic>α</jats:italic>,2<jats:italic>α</jats:italic>,3<jats:italic>β</jats:italic>,4<jats:italic>β</jats:italic>)‐2‐(3,4‐dimethoxyphenyl)‐4‐(3,4,5‐trimethoxyphenyl)cyclobutane‐1,3‐diyl]dicarbonyl}bis[5,6‐dihydropyridin‐2(1<jats:italic>H</jats:italic>)‐one]; <jats:bold>2</jats:bold>) were isolated from the stem of <jats:italic>Piper arborescens</jats:italic>, besides two known cyclobutanoid amides, piperarboresine (=1,1′‐{[(1<jats:italic>α</jats:italic>,2<jats:italic>α</jats:italic>,3<jats:italic>β</jats:italic>,4<jats:italic>β</jats:italic>)‐2‐(7‐methoxy‐1,3‐benzodioxol‐5‐yl)‐4‐(3,4,5‐trimethoxyphenyl)cyclobutane‐1,3‐diyl]dicarbonyl}bis[5,6‐dihydropyridin‐2(1<jats:italic>H</jats:italic>)‐one]; <jats:bold>3</jats:bold>) and piplartine‐dimer A (=1,1′‐{[(1<jats:italic>α</jats:italic>,2<jats:italic>α</jats:italic>,3<jats:italic>β</jats:italic>,4<jats:italic>β</jats:italic>)‐2,4‐bis(3,4,5‐trimethoxyphenyl)cyclobutane‐1,3‐diyl]dicarbonyl}bis[5,6‐dihydropyridin‐2(1<jats:italic>H</jats:italic>)‐one]; <jats:bold>4</jats:bold>). The structures of the two new compounds were determined by spectral analyses.