A diastereoselective cobalt-mediated synthesis of benzopyrans using a novel variation of an intramolecular Nicholas reaction in the key cyclisation step: Optimisation and biological evaluation

Journal of the Chemical Society - Perkin Transactions 1

Volumn , Issue 8, 1998, Pages 1427-1438

  Mann, Alastair ^a   Muller, Christophe ^a   Tyrrell, Elizabeth ^a  

^a KINGSTON UNIVERSITY   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 33748593959     PISSN: 0300922X     EISSN: None     Source Type: Journal    
DOI: 10.1039/a708264i     Document Type: Review

References (26)

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16. An intermolecular example: M. E. Krafft, Y. Y. Cheung, C. Wright and R. Cali, J. Org. Chem., 1996, 61, 3912.
17. Only trace quantities of the benzopy ran derivative, such as 12a, were observed by GCMS when the one-pot cyclisation procedure was employed.
18. NOE studies on the C-3 methine proton in both compounds 12a and 12b showed no enhancement in the signal when the C-4 benzylic proton was irradiated.
19. The importance of the cobalt cluster for maintaining both the efficiency and the selectivity of the Nicholas reaction see: K. M. Nicholas and P. J. Ganesh, J. Org. Chem., 1997, 62, 1737.
20. The one pot procedure can be monitored by TLC and in most instances is complete within 30 minutes; these reactions were left for 48 hours.
21. K. Ueda, S. Tanaka, K. Kagai, H. Ono, I. Ohtsuka, M. Kawase and T. Ohgah, USP 4874869, 1989 (Chem. Abstr., 1982, 97, 38 936a).
22. We are grateful to SKB (Harlow) for the generous donation of a sample of cromakalim.
23. 13C NMR spectra as well as IR, LRMS and in most examples HRMS that were consistent with the assigned structure. In general the cobalt clusters gave poorly resolved NMR spectra and so IR data alone are provided.
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25. G. M. Sheldrick, SHELXTL-PC, 1991, Release 4.2, Siemens Analytical X-Ray Instruments Inc., Madison, WI.
26. G. M. Sheldrick, SHELXL96, 1996, Program for Crystal Structure Refinement, University of Göttingen.