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. 2019 Jul 2;12(3):103. doi: 10.3390/ph12030103

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© 2019 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Scheme 2 — Reagents and conditions: (a) trifluoroacetic acid (TFA) (60% aq. soln.), room temp., 2 h, 83% (α/β = 1:0.9; (b) Ac₂O, py, room temp., 1.5 h, 69% (α/β = 1:0.5); (c) CH₃SO₂NH₂, BF₃·Et₂O, CH₂Cl₂/CH₃CN, room temp., 2 h, 81% (β/α = 1:0.4); (d) trimethylsilyl azide (TMSN₃), trimethylsilyl triflate (TMSOTf), CH₃CN, 65 °C, MW, max. 150 W, 1 h 40 min, 86% (13, β/α ratio, 1:0.8) and 14% (14); (e) P(OMe)₃, CH₂Cl₂, room temp., 23 h, 56% (α/β = 1:0.3).