Synthesis of alpha-halo enones and enals

1. A method for making an α-halo enone or enal comprising:

reacting a propargyl alcohol with an electrophilic halogen source in the presence of a gold catalyst complex and a metal co-catalyst complex to form an α-halo enone or α-halo enal.

2. The method of claim 1 wherein the α-halo enone or α-halo enal is defined by the formula:

where R 1 and R 2 each independently are hydrogen, a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl, or where R 1 and R 2 are covalently bonded to form a carbocyclic or heterocyclic ring; R 3 is hydrogen, a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl; and X is a halogen.

3. The method of claim 1 , wherein the propargyl alcohol is defined by the formula:

where R 1 and R 2 each independently are either hydrogen, a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl, or where R 1 and R 2 are covalently bonded to form a carbocyclic or heterocyclic ring; and R 3 is hydrogen, a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl.

4. The method of claim 2 wherein X is bromine or iodine.

5. The method of claim 3 wherein R 3 is hydrogen.

6. The method of claim 3 wherein R 3 is a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl.

7. The method of claim 1 , wherein the electrophilic halogen source is selected from a halo-succinamide, a halo-saccharin, trihaloisocyanuric acid, bromine, a mixed halogen, a hypervalent iodine moiety, or iodine in combination with an oxidant.

8. The method of claim 1 , wherein the gold catalyst complex is a gold (I) catalyst having the formula LAuY, wherein Au is gold, L is a ligand, and Y is a non-coordinating anion.

9. The method of claim 1 , wherein the gold catalyst complex is a Au(III) complex.

10. The method of claim 1 , wherein the metal co-catalyst complex includes a metal selected from vanadium, rhenium, tungsten, or molybdenum.

11. The method of claim 1 , wherein the propargyl alcohol is reacted with the electrophilic halogen source in the presence of the gold catalyst complex, the metal co-cataylst complex, a solvent, and an additive that facilitates suppression of a des-halo derivative.

12. The method of claim 11 , wherein the additive is selected from a sulfoxide, a phosphine oxide, a phosphoramide, an amide, a urethane, a urea, or water.

13. The method of claim 11 , wherein the solvent is an anhydrous solvent.

14. The method of claim 1 wherein the electrophilic halogen source is a halo-succinamide, the gold catalyst complex is Au(PPh 3 )NTf 2 , where Tf is F 3 (CSO 2 ), and the metal co-catalyst complex is MoO 2 (acac) 2 .

15. A method for producing an α-halo enone or enal comprising:

mixing a propargyl alcohol, an electrophilic halogen source, a gold catalyst complex, a metal co-catalyst complex, and a solvent; and

maintaining the mixture under suitable reaction conditions to convert the propargyl alcohol to a α-halo enone or enal.

16. The method of claim 15 , wherein the propargyl alcohol is defined by the formula:

where R 1 and R 2 each independently are either hydrogen, a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl, or where R 1 and R 2 are covalently bonded to form a carbocyclic or heterocyclic ring; and R 3 is hydrogen, a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl.

17. The method of claim 16 wherein R 3 is hydrogen.

18. The method of claim 16 wherein R 3 is a substituted- or unsubstituted-alkyl, a cycloalkyl, or an aryl.

19. The method of claim 16 , wherein the maintaining step comprises maintaining the mixture at a temperature from about 0° C. to about 60° C. to convert the propargyl alcohol to the α-halo enone or enal.

20. The method of claim 16 , wherein the mixing step comprises mixing the propargyl alcohol, the electrophilic halogen source, the gold catalyst complex, the metal co-catalyst complex, the solvent, and an additive that facilitates suppression of a des-halo derivative.