Allylic oxidations catalyzed by dirhodium catalysts under aqueous conditions
The present invention relates to compositions and methods for achieving the efficient allylic oxidation of organic molecules, especially olefins and steroids, under aqueous conditions. The invention concerns the use of dirhodium (II,II) “paddlewheel complexes, and in particular, dirhodium carboximate and tert-butyl hydroperoxide as catalysts for the reaction. The use of aqueous conditions is particularly advantageous in the allylic oxidation of 7-keto steroids, which could not be effectively oxidized using anhydrous methods, and in extending allylic oxidation to enamides and enol ethers.
1. A method for conducting oxidation of an allylic group of a compound, which comprises incubating a compound having an allylic group in the presence of:
(A) a mixed-valent dirhodium(II,III) catalyst (Rh 2 5+ ); and
(B) an aqueous solution of tert-butyl hydroperoxide
under conditions sufficient to oxidize said allylic group of said compound.
2. The method of claim 1 , wherein said mixed-valent dirhodium(II,III) catalyst (Rh 2 5+ ) is a member of the carboxamidate class of dirhodium(II,II) paddlewheel complexes.
3. The method of claim 2 , wherein the arms of said carboxamidate class of dirhodium(II,II) paddlewheel complexes comprises seven membered rings.
4. The method of claim 3 , wherein said mixed-valent dirhodium(II,III) catalyst (Rh 2 5+ ) is dirhodium(II,II) caprolactamate [Rh 2 (cap) 4 ].
5. The method of claim 1 , wherein said compound is dissolved in an organic solvent.
6. The method of claim 1 , wherein said organic solvent is dichloroethane or dichloromethane.
7. The method of claim 1 , wherein said mixed-valent dirhodium(II,III) catalyst (Rh 2 5+ ) is present in said incubation at 0.4-0.6 molar equivalents.
8. The method of claim 1 , wherein said tert-butyl hydroperoxide is present in said incubation at 9 or fewer molar equivalents.
9. The method of claim 1 , wherein said compound has a C 5 -C 12 alkenyl moiety which is optionally substituted with N, S, O or halogen, and that has said allylic group.
10. The method of claim 1 , wherein said compound has the structure:
and said method results in the production of a compound having the structure:
11. The method of claim 1 , wherein said compound has a cyclohexene moiety which is optionally substituted with N, S, O or halogen, and that has said allylic group or is bonded to a carbon having an allylic methylene group.
12. The method of claim 1 , wherein said compound has an aromatic moiety which is optionally substituted with N, S, O or halogen, and that has said allylic group or is bonded to a carbon having an allylic methylene group.
13. The method of claim 1 , wherein said compound has a steroidal moiety which is optionally substituted with N, S, O or halogen, and that has said allylic group, wherein said steroidal moiety has the structure:
wherein R is H or a C 2 -C 8 alkyl or alkenyl group which is optionally substituted with N, S, O or halogen, and R1 is O or a C 2 -C 8 alkyl or alkenyl group which is optionally substituted with N, S, O or halogen.
14. The method of claim 1 , wherein said compound has an enone moiety that has said allylic group.
15. The method of claim 1 , wherein said compound has an enamide moiety that has said allylic group.
16. The method of claim 1 , wherein said compound has an enol ether moiety that has said allylic group.