TY - JOUR
T1 - Protecting-Group-Free Site-Selective Reactions in a Metal–Organic Framework Reaction Vessel
AU - Huxley, Michael T.
AU - Burgun, Alexandre
AU - Ghodrati, Hanieh
AU - Coghlan, Campbell J.
AU - Lemieux, Anthony
AU - Champness, Neil R.
AU - Huang, David M.
AU - Doonan, Christian J.
AU - Sumby, Christopher J.
PY - 2018/5/23
Y1 - 2018/5/23
N2 - Site-selective organic transformations are commonly required in the synthesis of complex molecules. By employing a bespoke metal–organic framework (MOF, 1·[Mn(CO)3N3]), in which coordinated azide anions are precisely positioned within 1D channels, we present a strategy for the site-selective transformation of dialkynes into alkyne-functionalized triazoles. As an illustration of this approach, 1,7-octadiyne-3,6-dione stoichiometrically furnishes the mono-“click” product N-methyl-4-hex-5′-ynl-1′,4′-dione-1,2,3-triazole with only trace bis-triazole side-product. Stepwise insights into conversions of the MOF reaction vessel were obtained by X-ray crystallography, demonstrating that the reactive sites are “isolated” from one another. Single-crystal to single-crystal transformations of the Mn(I)-metalated material 1·[Mn(CO)3(H2O)]Br to the corresponding azide species 1·[Mn(CO)3N3] with sodium azide, followed by a series of [3+2] azide–alkyne cycloaddition reactions, are reported. The final liberation of the “click” products from the porous material is achieved by N-alkylation with MeBr, which regenerates starting MOF 1·[Mn(CO)3(H2O)]Br and releases the organic products, as characterized by NMR spectroscopy and mass spectrometry. Once the dialkyne length exceeds the azide separation, site selectivity is lost, confirming the critical importance of isolated azide moieties for this strategy. We postulate that carefully designed MOFs can act as physical protecting groups to facilitate other site-selective and chemoselective transformations.
AB - Site-selective organic transformations are commonly required in the synthesis of complex molecules. By employing a bespoke metal–organic framework (MOF, 1·[Mn(CO)3N3]), in which coordinated azide anions are precisely positioned within 1D channels, we present a strategy for the site-selective transformation of dialkynes into alkyne-functionalized triazoles. As an illustration of this approach, 1,7-octadiyne-3,6-dione stoichiometrically furnishes the mono-“click” product N-methyl-4-hex-5′-ynl-1′,4′-dione-1,2,3-triazole with only trace bis-triazole side-product. Stepwise insights into conversions of the MOF reaction vessel were obtained by X-ray crystallography, demonstrating that the reactive sites are “isolated” from one another. Single-crystal to single-crystal transformations of the Mn(I)-metalated material 1·[Mn(CO)3(H2O)]Br to the corresponding azide species 1·[Mn(CO)3N3] with sodium azide, followed by a series of [3+2] azide–alkyne cycloaddition reactions, are reported. The final liberation of the “click” products from the porous material is achieved by N-alkylation with MeBr, which regenerates starting MOF 1·[Mn(CO)3(H2O)]Br and releases the organic products, as characterized by NMR spectroscopy and mass spectrometry. Once the dialkyne length exceeds the azide separation, site selectivity is lost, confirming the critical importance of isolated azide moieties for this strategy. We postulate that carefully designed MOFs can act as physical protecting groups to facilitate other site-selective and chemoselective transformations.
UR - https://doi.org/10.1021/jacs.8b02896
U2 - 10.1021/jacs.8b02896
DO - 10.1021/jacs.8b02896
M3 - Article
SN - 0002-7863
VL - 140
SP - 6416
EP - 6425
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 20
ER -