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. Author manuscript; available in PMC: 2013 Jun 15.
Published in final edited form as: Bioorg Med Chem Lett. 2012 Apr 25;22(12):4018–4022. doi: 10.1016/j.bmcl.2012.04.084

Scheme 2.

Scheme 2

The synthesis of pyranoxanthones 14–21.

Reagents and conditions: (a) prenal/citral, Ca(OH)2, MeOH, rt, 36 h (14: 85%; 15: 70%). (b) prenal/citral, 140–150 ° C, 6 h (16: 95%; 17: 93%). (c) OsO4, NMMO, t-BuOH-THF-H2O (10:3:1), rt, 48 h (18: 85%; 19: 70%; 20: 19%; 21: 22%).