“Click” Synthesis of Nonsymmetrical Bis(1,2,3-triazoles)
摘要:
Unsymmetrically 1,1'-disubstituted 4,4'-bis-1H-1,2,3-triazoles 4 have been prepared from 4-ethynyl-1,2,3-triazoles 5 and azides. Following a "double-click" strategy, two complementary approaches were implemented for the preparation of the key 4-ethynyltriazole intermediates 5: (a) the stepwise Swern oxidation/Ohira-Bestman alkynylation of readily available 4-hydroxymethyl-1,2,3-triazoles 8 and (b) the stepwise cycloaddition of TMS-1,4-butadlyne 9. The method is highlighted by its compatibility with orthogonally protected and functionalized saccharide-peptide hybrids and its ability to be extended to the trisubstituted counterparts 12.
Cationic 1,2,3-Triazolium Alkynes: Components To Enhance 1,4-Regioselective Azide–Alkyne Cycloaddition Reactions
作者:Zaira Monasterio、Maialen Sagartzazu-Aizpurua、José I. Miranda、Yuri Reyes、Jesus M. Aizpurua
DOI:10.1021/acs.orglett.6b00055
日期:2016.2.19
thermal [3 + 2] cycloadditionreactions with azides roughly 50- to 100-fold faster than comparable noncharged alkynes. Further, the reaction is highly 1,4-regioselective (dr up to 99:1) owing to the selective stabilization of 1,4-TS transition states via conjugative π-acceptor assistance of the alkyne triazolium ring. The novel cationic triazolium alkynes also accelerate the CuAAC reaction to provide bis(1