CuI‐Catalyzed Alkyne–Azide “Click” Cycloadditions from a Mechanistic and Synthetic Perspective
Tóm tắt
Từ khóa
Tài liệu tham khảo
For reviews of click chemistry see:
Huisgen R., 1984, 1,3‐Dipolar Cycloadditional Chemistry
Peer M., 1998, Spec. Chem. Mag., 18, 256
Mulzer J., 1991, Org. Synth. Highlights, 77
For examples of uncatalyzed 1 3‐cycloaddition reactions between azides and alkynes see:
Bastide J., 1973, Bull. Soc. Chim. Fr., 2294
Stepanova N. P., 1985, Zh. Org. Khim., 21, 979
Stepanova N. P., 1989, Zh. Org. Khim., 25, 1613
For triazole cytokine inhibition see:
Bastide J., 1978, Chemistry of the Carbon—Carbon Triple Bond
Chan C.‐L., 1996, Chem. Commun., 2067
For examples of stable CuIcomplexes with ansp2carbon atom ligand see:
Yang X., 2004, Synlett, 13, 2303
Unpublished results reported by Fokin and co‐workers indicate that when CuIis quenched by air‐oxidation it can be regenerated by the reducing agent thus maintaining a low steady state concentration of CuIof 200 to 700 μMfor reactions in H2O/tBuOH; see ref.[21b]
Absence of an amine hydrochloride salt gave only trace products or recovered starting material after two hours; see ref.[40a]. For information on the dissolution of copper in aqueous systems and facilitation by amine hydrochloride salts see:
Thayer J. S., 1995, Adv. Organomet. Chem., 38, 71
Timms P. L., 1977, Adv. Organomet. Chem., 84
Jukes A. E., 1974, Adv. Organomet. Chem., 12, 228
From Sigma–Aldrich 25 g of Cu0nanopowder costs 92.40 compared to 12.40 for 25 g of copper sulfate pentahydrate and 7.10 for 25 g of reagent grade CuIiodide.
Alkyne homocoupling may result in lower yields in some substrates; see below section 3.4.1.
For examples of unprotected alcohols that undergo click reactions without problem see Table 1 Entries 2 and 3 and Table 5 Entry 4.
The poor enantioselectivity observed for azide39may result from suprafacial [3 3] sigmatropic migration of the azido group which would lead to racemization of the unconverted enantiomer.
This steric effect has been noted elsewhere; see: ref.[10].
Stuerga D., 2002, Microwaves in Organic Synthesis
Lidström P., 2004, Microwave‐Assisted Organic Synthesis
See ref.[59a]; two reactions conducted under both microwave conditions and at room temperature afforded the desired product in almost identical yields with microwave conditions only reducing reaction times.
David O. R. P., 2005, Chem. Commun., 4333
Only one example of CuIIsulfate reduction to catalyze triazole formation on the solid phase has been reported (see ref.[26b]).
Cadiot P., 1969, Chemistry of Acetylenes