Two new 9,10- seco limonoids with a central 3,4-dihydro-2 H-pyran motif, named xylomolones A and B (1 and 2, respectively), possessing identical absolute configurations but reversed alignments of ring A, compared to the tricyclic core of rings B-D, were obtained from seeds of the Thai mangrove Xylocarpus moluccensis, together with a highly modified 1,2- seco limonoid, named xylomolone C (3), containing a novel 3-oxabicyclo[3.2.1]octane-2,7-dione motif, and a new C11-terpenic acid methyl ester (4). The relative and absolute configurations of 1-4 were evidenced by extensive nuclear magnetic resonance (NMR) investigations combined with density functional theory and time-dependent density functional theory calculations of electronic circular dichroism, specific optical rotation, and 13C NMR data. The co-isolation of 1-4 allowed us to propose a novel convergent strategy for limonoid biosynthesis for the first time. This study demonstrates that mangroves of the genus Xylocarpus harbor new limonoid biosynthetic routes.