Pyridine borane complexes
The present invention relates to new borane complexes with substituted pyridines, a process for the synthesis of new borane complexes with substituted pyridines, solutions comprising new borane complexes with substituted pyridines and a method of using new borane complexes with substituted pyridines for organic reactions.
1. A borane complex of the formula (1)
wherein
R 1 and R 2 represent independently from each other C 1 -C 8 -alkyl, C 1 -C 8 -alkoxy, C 1 -C 8 -alkoxy-C 1 -C 8 -alkyl or halogen, with the provision that R 1 and R 2 are not simultaneously methyl.
2. The borane complex according to claim 1 , wherein R 2 is bonded to the 5-position of the pyridine ring.
3. The borane complex according to claim 2 , wherein R 1 is methyl and R 2 is ethyl.
4. The borane complex according to claim 1 , wherein the substituted pyridine is 5-ethyl-2-methylpyridine, 4-ethyl-2-methylpyridine, 3-ethyl-2-methylpyridine, 2,5-diethylpyridine, 5-propyl-2-methylpyridine, 4-propyl-2-methylpyridine, 5-isopropyl-2-methylpyridine, 5-t-butyl-2-methylpyridine, 5-n-hexyl-2-methylpyridine, 4-isobutyl-2-methylpyridine, 2,4-dipropylpyridine, 5-methoxymethyl-2-methylpyridine or 5-ethoxymethyl-2-methylpyridine.
5. The borane complex according to claim 1 , wherein the substituted pyridine is 5-ethyl-2-methylpyridine.
6. A solution comprising at least one of the borane complexes according to claim 1 and at least one solvent.
7. The solution according to claim 6 , wherein the solvent comprises the substituted pyridine used to complex the borane in formula (1).
8. The solution according to claim 6 , wherein the concentration of the borane complexes is between 0.05 and 6.5 mol/l.
9. The solution according to claim 8 , wherein the solvent is tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfide, 1,6-thioxane, toluene, hexane or cyclohexane.
10. A process to synthesize the borane complex according to claim 1 , comprising reacting a borane source with a substituted pyridine.
11. An organic reaction which comprises contacting the borane complex according to claim 1 with a substrate in a reaction vessel.
12. The reaction according to claim 11 , wherein the organic reaction is a reduction of a functional group or a hydroboration reaction with alkenes and alkynes.
13. A method for reductive amination of an aldehyde or a ketone which comprises using a primary or secondary amine with the borane complex according to claim 1 .