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Hydration and hydroamination of 1-alkynes with....
« on: June 19, 2003, 10:30:00 PM »

Riken Review No. 42, pp 53-56 (2001)

(https://www.thevespiary.org/rhodium/Rhodium/pdf/ruthenium.hydroamination.1-alkynes.pdf)

Ruthenium complexes that efficiently catalyze hydration and hydroamination of 1-alkynes have been found. The hydration described here is the first example of anti-Markovnikov regioselectivity to produce aldehydes. A mechanism involving Ru(IV)-hydride-vinylidene intermediate is proposed. A highly practical catalytic hydroamination method has also been developed which was applied to synthesis of nitrogen containing heterocycles.

Summary:

We have applied the present catalytic hydroamination to the synthesis of nitrogen heterocycles, such as quinolines4) and indoles.6) In particular the indole synthesis is highly valuable because the reaction can employ inexpensive unsubstituted anilines. Almost all other known methods require derivatization of anilines. Even Fischer method, which is regarded as the most practical method, requires conversion of anilines to unstable and toxic hydrazines. Applying our catalytic hydroamination system to the reaction of anilines and 1-subsituted-2-propyne-1-ols (Scheme 6) at slightly higher temperature (140ßêC), 3-methyl-2-substituted indoles were formed regioselectively. Regioselective synthesis of this kind of indoles is di•cult by Fischer method. From the viewpoint of green chemistry, the process is also favorable because it yields only H2O as the stoichiometric by-product.

References

1) M. Tokunaga and Y.Wakatsuki: Angew. Chem., Int. Ed. Engl. 37, 2867 (1998).
2) M. Tokunaga and Y. Wakatsuki: J. Synth. Org. Chem. Jpn. 58, 587 (2000).
3) T. Suzuki, M. Tokunaga, and Y. Wakatsuki: Org. Lett. 3, 735 (2001).
4) M. Tokunaga, M. Eckert, and Y. Wakatsuki: Angew. Chem., Int. Ed. Engl. 38, 3222 (1999).
5) F. Takei et al.: Chem. Eur. J. 6, 983 (2000).
6) M. Tokunaga, M. Ota, M. Haga, and Y. Wakatsuki: Tetrahedron. Lett. 42, 3865 (2001).