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. Author manuscript; available in PMC: 2012 Jul 31.
Published in final edited form as: J Am Chem Soc. 2008 Dec 3;130(48):16295–16309. doi: 10.1021/ja804659n

Scheme 13.

Scheme 13

Model studies of final C20–C21 sulfone fragment coupling and product elaboration. Reagents and conditions: a) EtMgBr, THF, −78 °C, 99%; b) TMSCH2Li, THF, −78 °C, 70%; c) KH, THF, 99%; d) H2O2, Na2WO4·2H2O,72 MeOH, 91%; e) 81 (1 equiv), LDA (1.2 equiv), THF, then 82 (1.5 equiv), −78 °C, dr(C21): 6:1, 51% 83; f) PhSLi, Et2O, −78 °C, 99%; g) KHBEt3, THF, −78 to −20 °C, dr 5–6:1, 56% major isomer; h) HgCl2, pH 7 buffer, MeCN/THF, 0 °C, 86%; i) KHBEt3, CH2Cl2, −78 to −20 °C, dr 10:1, 91% major isomer. See ref31 for abbreviations.