Cp*(2)TiMe(2): an improved catalyst for the intermolecular addition of n-alkyl- and benzylamines to alkynes.
Cp(2)TiMe(2) has been found to be a competent catalyst for the intermolecular addition of sterically less demanding n-alkyl- and benzylamines to internal alkynes. In the presence of 2.0-6.0 mol % of the catalyst, hydroamination reactions between n-propyl-, n-hexyl-, benzyl-, p-methoxybenzyl- or 2-phenylethylamine and diphenylacetylene, 3-hexyne or 4-octyne go to completion within 24 h or less at 114 degrees C (oil bath temperature). After subsequent reduction of the initially formed imines with zinc-modified sodium cyanoborohydride in MeOH at 25 degrees C, the corresponding secondary amines can be isolated in excellent yields (>78%). Hydroamination/reduction sequences employing the unsymmetrically substituted alkyne 1-phenylpropyne give access to mixtures of regioisomeric secondary amines. The observed regioselectivity is low.
Heutling
Andreas
A
Institut für Organische Chemie, Universität Hannover, Schneiderberg 1B, D-30167 Hannover, Germany.
Doye
Sven
S