Triconoids A–D, Four Limonoids Possess Two Rearranged Carbon Skeletons from Trichilia connaroides

Four limonoids, triconoids A–C (1–3) possessing a new rearranged mexicanolide skeleton and triconoid D (4) furnishing a new rearranged 1,2-seco-phragmalin skeleton, were isolated from the Nepalese plant Trichilia connaroides. Two rearranged limonoid skeletons sharing an F ring of methyl 5-oxotetrahydrofuran-2-carboxylate were postulated to be formed biosynthetically via a very unique chemical cascade. Their structures were fully accomplished by spectroscopic data, single-crystal X-ray diffraction, and electrostatic circular dichroism analysis.