CRYSTAL-STRUCTURES, CHIRALITIES AND PHOTOCHEMISTRY OF 2 POLYMORPHS OF L-PROLINOLIUM ALPHA-ADAMANTYLACETOPHENONE-P-CARBOXYLATE

The absolute stereochemical course of the photochemical rearrangement reactions of alpha-adamantylacetophenones has been studied by crystal structure analyses of two polymorphs of L-prolinolium alpha-adamantylacetophenone-p-carboxylate and of a crystal containing the major photoproduct, and by correlation of the crystal structure data with photochemical behaviour. Crystal data are: T = 295 K, Cu K alpha, lambda = 1.54178 Angstrom. L-Prolinolium alpha-adamantyl-acetophenone-4-carboxylate, C24H33NO4, C5H12NO+.C19H21O3(-) M(r) = 399.53; needle form, P2(1)2(1)2(1), a = 17.266 (2), b = 19.292(3), c = 6.3739 (9) Angstrom, Z = 4, R = 0.041 for 1583 reflections with I > 3 sigma(I); plate form, P2(1)2(1)2(1), a = 11.798 (1), b = 43.563(3), c = 8.4434 (8) Angstrom, Z = 8 (two molecules per asymmetric unit), R = 0.056 for 3565 reflections. Photoproduct (crystals are a 1:1 complex of reactant and photoproduct), C48H68N2O9 (C24H33NO4.C24H33NO4.H2O), M(r) = 817.08, P2(1)2(1)2(1), a = 11.021 (2), b = 56.481 (8), c = 6.840 (1) Angstrom, Z = 4, R = 0.10 for 1920 reflections. The two polymorphs of the adamantylacetophenone derivative contain molecules with dimensions and conformations similar to those of previously studied analogues. Both polymorphs have chiral space groups, with the absolute chirality determined from that of the (known) L-prolinolium cation. The needle form of the material (Z = 4) contains only one conformational enantiomer of the adamantylacetophenone anion; in the plate form (Z = 8), however, the anion exists in both conformational chiralities, as crystallographically independent units. The observation of a large enantiomeric excess in the photoproduct derived from the needle form and a much reduced excess in that derived from the plate form can be correlated with these structural observations. The absolute chirality of the photoproduct from the needle form has been correlated with the absolute chirality of the reactant via a proposed reaction pathway.