13C NMR chemical shift assignment based on 13C INADEQUATE and heteronuclear 13C, 1H-COSY experiments and absolute configuration of a new chiral pentacyclic pinocarvone dimer

13 C NMR chemical shift assignment based on two-dimensional homonuclear 13C–13C Incredible Natural Abundance Double Quantum Transfer Spectroscopy (INADEQUATE) and heteronuclear 13C–1H chemical shift correlation spectroscopy (C, H-COSY) experiments together with the absolute configuration based on X-ray crystallographic analysis of a previously unknown pentacyclic dimerization product of (1S)-pinocarvone, (2S, 5S, 1′S)-6, 6, 6′,6′-tetramethyl-3, 4, 5, 6, 7, 8-hexahydro-5,7-methanospiro{2H-1-benzopyran-2,2′-bicyclo[3.1.1]heptan}-3′-one, C20H28O21, are presented. The Diels–Alder dimerization produces a new chiral centre with a definite absolute configuration from the dimerizing (1S)-pinocarvone molecules during the ring formation.