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. Author manuscript; available in PMC: 2009 Jan 8.
Published in final edited form as: J Am Chem Soc. 2006 Sep 13;128(36):11906–11915. doi: 10.1021/ja062364i

Scheme 6a.

Scheme 6a

a Reagents and conditions: (a) Ph2SO, Tf2O, TBP, CH2Cl2; 43 (55%); (b) 41, Ph2SO, Tf2O, TBP, CH2Cl2; add 52 (88%); (c) TBAF, THF (98%); (d) Ph2SO, Tf2O, TBP, CH2Cl2; add 51 (85%); (e) K2CO3, MeOH (91%).