Photochemical methods of making cyclobutane boronates and related compounds
The present technology relates generally cyclobutane boronates, including methods of preparation by exposing a mixture of a compound of Formula I in a solvent and a catalytic amount of a visible light sensitizer to provide a compound of Formula II, stereoisomers thereof, and/or salts of any of the foregoing. The cyclobutane boronate compounds are useful intermediates in the preparation of pharmaceutically active compounds as well as other useful compounds.
1. A method for making cyclobutane boronates comprising exposing a mixture of a compound of Formula I in a solvent
and a catalytic amount of a visible light photosensitizer to provide a compound of Formula II, stereoisomers thereof, and/or salts of any of the foregoing,
wherein
X is —(CR 11 2 ) n —O—(CR 11 2 ) p —, —(CR 11 2 ) n —NR 12 —(CR 11 2 ) p — or a C 3 -C 4 alkylene group,
wherein R 11 at each occurrence and R 12 are independently H or C 1-6 alkyl, and
each of n and p is independently 1 or 2;
Y 1 and Y 2 are independently selected from O, CR 7 2 , or NR 7 ; or Y 1 and Y 2 are both F and the boron atom forms a fluoride salt with a third fluorine atom and an alkali metal cation;
Z 1 and Z 2 are independently selected from a substituted or unsubstituted H or a substituted or unsubstituted C 1-12 alkyl, C 2-12 alkenyl, aryl, aralkyl, heteroaryl, or heteroaralkyl group, or Z 1 and Z 2 together form Z, wherein Z is selected from a substituted or unsubstituted C 2 -C 12 alkylene, C 2 -C 12 heteroalkylene, or phenylene group;
R 1 is a substituted or unsubstituted alkenyl, alkynyl, aryl, or heteroaryl group;
R 2 , R 3 , R 4 and R 5 are each independently H or a substituted or unsubstituted alkyl group;
R 6 and R 7 at each occurrence are independently selected from H, a substituted or unsubstituted aryl or aralkyl group, or a R 8 SO 2 , R 9 OC(O), or R 10 C(O) group; and
R 8 , R 9 and R 10 at each occurrence are independently selected from a substituted or unsubstituted alkyl, aryl, or aralkyl group.
2. The method of claim 1 , wherein the visible light photosensitizer is an iridium(III) photosensitizer.
3. The method of claim 1 , wherein the catalytic amount of visible light photosensitizer is 0.025 mol % to 5 mol % of the compound of Formula I.
4. The method of claim 1 , wherein the photosensitizer is [Ir(2′,4′-dF-5-CF 3 -ppy) 2 (4,4′-dtb-bpy)] + .
5. The method of claim 1 , wherein the solvent is dichloromethane, DMSO, DMF, acetone, methanol, THF, ether, hexanes, or a mixture of any two or more thereof.
6. The method of claim 1 , wherein the wavelength of visible light is 380 to 600 nm.
7. The method of claim 1 , wherein the energy of the visible light is at least 40 kcal/mol photons.
8. The method of claim 1 , wherein the concentration of the compound of Formula I is less than or equal to 0.05 M.
9. The method of claim 1 , wherein the visible light photosensitizer is a ruthenium(II) photosensitizer.