Structure of a hetero-Diels–Alder adduct

(6aRS,8RS, 10aRS)-4,6,6a,7,8,9,10,10aOctahydro-2,4,6,6,8-pentamethyl1H-[ 2]benzopyrano[3 ,4-d]pyrimidinel ,3(2H)-dione, CI6H24N203, M , = 292.38, triclinic, P1, a = 7 . 7 5 9 (1), b = 8 . 3 1 3 (2), c -12.985 (2)A, tx=90.08 (2), f l = 9 8 . 3 8 (2), y = 113.24 (2) °, V = 759.8 A 3, Z 2, D x = 1.274 Mg m -3, 2(Mo Ka) = 0.71069 A, /~ = 0.08 mm -~, F(000) = 316, T = 298 K, R = 0.050 for 2229 observed reflections. The structure was investigated to determine the relative configuration which could not be established unambiguously by NMR. The trans-fused cyclohexane ring adopts a chair conformation, whereas the dihydropyran ring takes a twisted half-chair form. 0108-2701/89/010167-02503.00 Experimental. Crystal size 0.2 × 0.4 x 0.8 mm. StoeSiemens four-circle diffraqtometer, monochromated Mo Ka radiation, profile-fitting mode involving variable scan width and speed (Clegg, 1981). 3914 reflections measured, 2Oma × = 50 °, h -9-*9, k -9 -*9 , 10-*15, three check reflections with no significant intensity change. 2668 unique reflections (R~,t= 0.059), of which 2229 with F > 4tr(F) were used for all calculations [SHELXS86 (Sheldrick, 1985); SHELX76 (Sheldrick, 1976)]. Cell constants refined from +20 values of 36 reflections in the range 20--25 ° . Absorption correction was not necessary. Extinction correction was performed yielding a secondary-extinction coefficient x of 0.013 (3), where Fc* = F c (1 + © 1989 International Union of Crystallography 168 A HETERO-DIELS-ALDER ADDUCT Table 1. Atomic coordinates (x 104) and equivalent isotropic displacement parameters (A 2 x 10 3) X y z Ueq* C(4a) 7239 (3) 4096 (2) 3908 (1) 31 (1) 0(5) 6930 (2) 5261 (2) 3284 (I) 38 (1) C(3) 7754 (3) 3595 (2) 5732 (1) 36 (1) C(I) 7396 (3) 1363 (2) 4360 (1) 38 (1) N(2) 7692 (2) 1995 (2) 5410 (1) 39 (1) 0(3) 8006 (2) 4075 (2) 6648 (1) 51 (1) N(4) 7493 (2) 4637 (2) 4942 (1) 35 (1) C(10a) 7181 (3) 2135 (2) 2443 (I) 32 (1) C(7) 7110 (3) 3309 (2) 662 (1) 37 (1) C(10b) 7296 (3) 2571 (2) 3586 (1) 32 (I) C(8a) 8072 (4) 2020 (3) -792 (2) 57 (1) O(1) 7238 (2) -132 (2) 4176 (1) 56 (1) C(8) 8484 (3) 2546 (3) 370 (1) 40 (1) C(6) 6255 (3) 4721 (2) 2164 (1) 35 (1) C(2) 7889 (4) 833 (3) 6224 (2) 59 (I) C(6a) 7439 (3) 3780 (2) 1835 (1) 32 (1) C(9) 8400 (3) 1010 (3) 1028 (2) 45 (1) C(10) 8662 (3) 1456 (3) 2202 (1) 41 (1) C(4) 7508 (3) 6343 (3) 5249 (2) 43 (1) C(6Y) 6646 (3) 6462 (3) 1684 (2) 50 (1) C(6X) 4131 (3) 3608 (3) 2030 (2) 47 (1) * Equivalent isotropie U defined as one third of the trace of the orthogonalized U u tensor. 0 .002xFc2/s in20) -°'25. Structure solution by direct methods. Refinement on F to R = 0.050, wR = 0.074; all non-H atoms anisotropic, H atoms were included using a riding model [C--H 0.96 A, U(H) = 0.08 A 2, except for methyl protons U(H) = 0.12 A2], 191 parameters, S = 2.49, weighting scheme w -~ = o2(F) + 0.0005F 2 which led to a featureless analysis of variance in terms of sin0 and F o, max. A/tr = 0.001, max. and min. heights in final Ap map 0.30 and -0 .16 e A -3 respectively. Atomic scattering factors from International Tables for X-ray Crystallography (1974). The site occupation factors for the two components of the disordered methyl group C(4) were initially refined (with their sum fixed at 1) and then fixed; an idealized hexagon was employed for the H-atom positions with U(H) = 0.08 A 2. Atomic parameters are given in Table 1, selected bond distances and angles in Table 2.* Fig. 1 shows a thermal-ellipsoid plot with the atom numbering. Related literature. For the preparation of some related compounds via a tandem-Knoevenagel-hetero-DielsAlder reaction see Brumby (1987), Tietze (1984) and Tietze, Stegelmeier, Harms & Brumby (1982).