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. Author manuscript; available in PMC: 2013 Jan 16.
Published in final edited form as: Angew Chem Int Ed Engl. 2011 Dec 7;51(3):728–732. doi: 10.1002/anie.201107623

Scheme 3.

Scheme 3

Synthesis of bis-sulfenylated diketopiperazine derivatives 34 and 36 and formation of O,S-acetal diketopiperazine 37. Reagents and conditions: a) NaHMDS (0.6 M in PhMe, 3.0 equiv), S8 (1.0 equiv), THF, 25 °C, 1 min; then 33 (1 M in THF, 1.0 equiv) 1 min; then NaHMDS (0.6 M in PhMe, 2.0 equiv), 25 °C, 0.5 h; b) NaBH4 (25 equiv), THF/MeOH (1:1), 0→25 °C, 0.75 h; c) PivCl (50 equiv), 25 °C, 15 h, 35%; d) Mg(OMe)2 (20 equiv), MeOH, 25 °C, 15 h, 87%; e) SEMCl (50 equiv), 25 °C, 15 h, 40%; f) SnCl4 (1.0 M in CH2Cl2, 14 equiv), CH2Cl2, 25 °C, 15 min, 93%.