Imino Diels±Alder adducts. XII. Two pyrano[3,2-c]quinolines K. Ravikumar, a * B. Sridhar, a M. Mahesh b and V. V. Narayana Reddy b a Laboratory of X-ray Crystallography, Indian Institute of Chemical Technology, Hyderabad 500 007, India, and b Organic Chemistry Division II, Indian Institute of Chemical Technology, Hyderabad 500 007, India Correspondence e-mail: ravikumar_iict@yahoo.co.in Received 20 July 2006 Accepted 28 July 2006 Online 23 August 2006 The crystal structures of pyranoquinolines 9-¯uoro-5-phenyl- 3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline, C 18 H 18 - FNO, and 9-methyl-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H- pyrano[3,2-c]quinoline, C 19 H 21 NO, are isomorphous. In both structures, the pyran ring is exo to the six-membered N- heterocyclic ring formed in the cycloaddition step. The torsion angles across the phenyl linkage for the two structures are 91.2 (1) and 88.3 (2)  . The striking feature in both crystal packings is that they do not contain the expected conventional hydrogen bonds, in spite of the presence of good hydrogen- bonding functionalities. Possible CÐH interactions are, however, observed. Comment Pyranoquinoline systems are of interest because they consti- tute the parent ring structure of pyranoquinoline alkaloids, such as khaplofoline, simulenoline and zanthodiaoline. A range of biological activities have been reported for pyrano- quinolines and their derivatives (Yamada et al., 1992; Nesterova et al., 1995), and these compounds are used as building blocks for the synthesis of various bridgehead N- heterocycles (Faber et al., 1984). Pyranoquinolines possess a diverse array of structural patterns in linear or angular forms, which provide to the organic chemist a challenging ®eld for investigations of their structures and accomplishment of their syntheses. Imino Diels±Alder reactions catalyzed by Lewis acids are a powerful and ef®cient methodology for the construction of nitrogen-containing heterocyclic compounds. Recently, the synthesis of disubstituted pyrano- and furo- quinolines by the application of imino Diels±Alder reactions between N-benzylideneanilines as dienes and 3,4-dihydro- pyran or 2,3-dihydrofuran as dienophiles, using ZrCl 4 as a catalyst, have been reported (Mahesh et al., 2004). We have been investigating how the formation of endo/exo isomers via Diels±Alder cycloadditions depends on the relative orienta- tion of the diene and the dienophile. In the course of these studies, the crystal structures of the title compounds, (Ia) and (Ib), have been determined. Compounds (Ia) and (Ib) have isomorphous crystal struc- tures (Figs. 1 and 2), despite one having F (electron with- drawing) and the other having CH 3 (electron donating) substituents; the difference in volume is also signi®cant (9.6 A Ê 3 for F and 23.5 A Ê 3 for CH 3 ; Kitaigorodsky, 1973; Bertault et al., 1998). The geometries of the molecules are very similar; differences ranging from 1.7 to 4.9  in bond angles involving atom C9 (Tables 1 and 2) may be attributed to the nature of the substituent (F or CH 3 ). The CÐF bond distance in (Ia) [1.3691 (15) A Ê ] agrees well with the mean value for CÐF distances for mono¯uoroarenes tabulated by Allen et al. (1987) [1.363 (8) A Ê ]. The structures reveal that the dihydropyran ring is attached to the central N-heterocyclic ring in an exo (trans) fashion [C5ÐC4ÐC12ÐO1 = 178.2 (1)  for (Ia) and 179.6 (1)  for (Ib)]. The H4ÐC4ÐC12ÐH12 torsion angle of 51.3  in (Ia) and 52.6  in (Ib) indicates that the junction between the pyran and quinoline rings is cis . Similarly, the orientation of atoms H5 and H4, de®ned by the H5ÐC5ÐC4ÐH4 torsion angle organic compounds o574 # 2006 International Union of Crystallography DOI: 10.1107/S0108270106029465 Acta Cryst. (2006). C62, o574±o576 Acta Crystallographica Section C Crystal Structure Communications ISSN 0108-2701 Figure 1 A perspective view of the molecule of (Ia). Displacement ellipsoids are drawn at the 30% probability level and H atoms are drawn as small circles of arbitrary radii.