Accelerated amide and ester reductions with amine boranes and additives
In a process for the accelerated reduction of organic substrates, selected from the group consisting of esters, amides, nitriles, acids, ketones, imines or mixtures thereof, they are reacted with an amine borane, sulfide borane or ether borane complex as a borane source in the presence of organic accelerator compounds containing either Lewis acidic or Lewis basic sites in their structure, of which the Lewis acidic site can coordinate with the carbonyl or nitrile or imine group of the substrate or the Lewis basic site can coordinate with the borane.
1. A process for the reduction of organic substrates, selected from the group consisting of esters, amides, nitriles, acids, ketones, imines or mixtures thereof, by reacting with an amine borane as a borane source in the presence of organic accelerator compounds different from the amine borane containing Lewis basic sites in their structure, of which the Lewis basic site is available to coordinate with the borane, wherein the organic accelerator compound containing Lewis basic sites is selected from the group consisting of Lewis basic sulfides, sulfoxides and tertiary amines.
2. A process as claimed in claim 1 , wherein esters, acids and ketones are reduced to give alcohols, and amines, nitriles and imines are reduced to give amines.
3. A process as claimed in claim 1 , wherein the amine borane is derived from amines which conform to the formulae
wherein R 5 -R 8 independently are C 1-6 -alkyl, phenyl, or in which each two of R 5 and R 6 independently can together form an C 4-6 -alkylene group, and R 5 -R 8 can be substituted by halogen and R 7 , R 8 can also be hydrogen.
4. A process as claimed in claim 3 , wherein the amine borane is N,N-diethylaniline borane (DEANB).
5. A process as claimed in claim 1 , wherein the organic substrate contains 4 to 30 carbon atoms.
6. A process as claimed in claim 5 , wherein the organic substrate contains one or more of alkyl, aryl, aralkyl, alkaryl, heterocycloalkyl and heteroaryl groups besides the ester, amide, nitrile, acid, keto or imino functional group and may contain other functional groups not reduced by borane.
7. A process as claimed in claim 5 , wherein the esters, amides, nitriles, acids, ketones and imines conform to the formulae
R 1 —C(═O)—OR 2
R 1 —C(═O)—NR 3 R 4
R 1 —CN
R 1 —C(═O)OH
R 1 —C(═O)—R 2
R 1 R 2 C═NH R 1 R 2 C═NR 3
wherein
R 1 -R 4 independently are C 1-12 -alkyl, C 6-12 -aryl, C 7-12 -aralkyl, C 7-12 alkaryl, heterocycloalkyl and heteroaryl and may contain other functional groups not reduced by borane.
8. A process as claimed in claim 1 , wherein the tertiary amines are sterically hindered and the amines, sulfides and sulfoxides contain C 1-12 -alkyl, C 6-12 -aryl, C 7-12 -alkaryl or C 7-12 -aralkyl groups, which in the case of amines and sulfides can also form a ring structure which may include O, S or N as heteroatoms.
9. A process as claimed in claim 8 , wherein the tertiary amine contains at least one residue selected from the group consisting of phenyl, which can be substituted, and branched alkyl.
10. A process as claimed in claim 1 , wherein the amount of accelerator compound, based on the amine borane is 0.01 to 100 mol-%.