Journal of the American Chemical Society
Communication
compare the results with the experimental data obtained for the crystal
structure of cycloalkyne−copper(I) complex 10. See the Supporting
Information.
(14) Fields, E. K. Arynes. In Organic Reactive Intermediates;
McManus, S. P., Ed.; Academic Press: New York, 1973; p 475.
(15) Wong, H. N. C.; Garratt, P. J.; Sondheimer, F. J. Am. Chem. Soc.
1974, 96, 5604−5605.
(16) Rodionov, V. O.; Presolski, S. I.; Díaz, D. D.; Fokin, V. V.; Finn,
M. G. J. Am. Chem. Soc. 2007, 129, 12705−12712.
(17) The structure of triazole 16 was confirmed by further
transformation. The reaction of 16 with ethyl azidoacetate without
the copper catalyst afforded bistriazole in 89% yield, which was
different from the product obtained from unprotected diyne 15 by the
sequential double-click reaction, i.e. strain-promoted cycloaddition
with azide 6 followed by CuAAC reaction with ethyl azidoacetate. See
the Supporting Information for details.
(18) Preliminary studies suggested the applicability of the protection
method to unstrained internal alkynes. For example, pretreatment of a
mixture of dimethyl acetylenedicarboxylate (DMAD) and phenyl-
acetylene with (MeCN)4CuBF4 in THF followed by the addition of
benzyl azide and TBTA and heating the reaction mixture at 65 °C for
24 h afforded the CuAAC product, 1-benzyl-4-phenyl-1H-1,2,3-
triazole (quant.), with recovery of DMAD (52%). In this case,
Huisgen cycloaddition between DMAD and benzyl azide did not
proceed, although the cycloadduct was obtained in 61% yield when the
reaction was performed without premixing with copper. See the
Supporting Information for details.
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(11) Given that cycloaddition with azide did not proceed, the
equilibrium between the complexed and uncomplexed cyclooctyne
would be dominated by the side of the 1:1 cycloalkyne−copper
complex even in the presence of a terminal alkyne, although the details
are yet to be investigated.
(12) The recrystallization of copper complex 10 was performed using
solvents from a bottle without special drying.
(13) We optimized the structure of dibenzo-fused cyclooctyne 5
using the DFT method at the B3LYP/6-31G(d) level in order to
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