Synthesis and Rearrangement of Quinone-Embedded Epoxycyclopentenones: A New Avenue to Pyranonaphthoquinones and Indenopyranones Saroj R. De, Sujit K. Ghorai, and Dipakranjan Mal* Department of Chemistry, Indian Institute of Technology, Kharagpur, India 721302 dmal@chem.iitkgp.ernet.in ReceiVed September 10, 2008 The epoxyquinones (e.g., 24), readily assembled in one step from the quinols (e.g., 27) by a simplified version of the Dowd oxidation, are shown to undergo rearrangement to pyranonaphthoquinones (e.g., 28) and their ring contracted homologues (e.g., 29) on flash vacuum pyrolysis at 450 °C and 0.01 Torr. The rearrangement has been demonstrated to be useful for a regiospecific synthesis of lambertellin (3). Similarly, the masked aziridinocyclopentanone 9 rearranges to 2-pyridone (37). Introduction The thermal rearrangement of epoxycyclopentenones to pyrones has been studied in detail from the mechanistic viewpoint. 1,2 It is established that an uncommon pericyclic reaction ( 4 π a + 2 π a process) 3 operates to form transient vinyl ketene intermediates, which in turn cyclize to 2-pyrones via a 4 π s + 2 π s process. The reaction, however, has not received any attention from synthetic chemists. 4 The inaccessibility of the starting epoxides and the stringent reaction conditions have probably hindered the advancement of the reaction. 5 A few years ago, we utilized the rearrangement as a means for the synthesis of isocoumarins and benzoisocoumarins, and extended it to a regiospecific total synthesis of coriandrin, a furoisocoumarin natural product. 6 Our continued interest in the synthesis of quinonoids 7 prompted us to explore the possibility of extending the reaction to the synthesis of chemically sensitive pyranon- aphthoquinone natural products, 1-5 8,9 (Figure 1). The chemistry of pyrones, particularly fused ones, is of current interest and has recently been reviewed. 10 Naphtho- (1) Ullman, E. F. J. Am. Chem. Soc. 1963, 85, 3529–3530. (2) (a) Dunston, J. W.; Yates, P. Tetrahedron Lett. 1964, 505–507. (b) Klunder, A. J. H.; Bos, W. J.; Verlaak, M. M.; Zwanenburg, B. Tetrahedron Lett. 1981, 22, 4553–4556. (3) (a) Morris, M. R.; Waring, A. J. Chem. Commun. 1969, 526–527. (b) Trauner, D.; Malerich, J. P.; Maimone, T. J.; Elliott, G. L. J. Am. Chem. Soc. 2005, 127, 6276–6283. (4) Houwen-Claassen, A. A. M.; Klunder, A. J. H.; Zwanenburg, B. Tetrahedron 1989, 45, 7134–7148. (5) (a) Chapman, O. L.; Hess, T. C. J. Org. Chem. 1979, 44, 962–964. (b) Undheim, K.; Nilson, B. P. Acta Chem. Scand. B 1975, 29, 503–506. (6) Mal, D.; Bandyopadhyay, M.; Ghorai, S. K.; Datta, K. Tetrahedron Lett. 2000, 41, 3677–3680. (7) Mal, D.; Patra, A.; Pahari, P.; Roy, S. J. Org. Chem. 2005, 70, 9017– 9020. (8) (a) Armstrong, J. J.; Turner, W. B. J. Chem. Soc. C 1965, 5927–5930. (b) Brown, P. M.; Krishnamoorthy, V.; Mathieson, J. W.; Thomson, R. H. J. Chem. Soc. C 1970, 109–110. (c) Poulton, G. A.; Bushnell, G. W.; Li, Y. L. Can. J. Chem. 1992, 70, 2688–2692. (d) Keniry, M. A.; Poulton, G. A. Magn. Reson. Chem. 1991, 29, 46–48. (e) Jones, G. B.; Qabaja, G. J. Org. Chem. 2000, 65, 7187–7194. (9) Rueping, M.; Sugiono, E.; Merino, E. Angew. Chem., Int. Ed. 2008, 47, 3046–3049. FIGURE 1. Representative structures of pyranonaphthoquinones. 10.1021/jo801961w CCC: $40.75  2009 American Chemical Society 1598 J. Org. Chem. 2009, 74, 1598–1604 Published on Web 01/13/2009