| 15809987 |
Hua R, Onozawa SY, Tanaka M: Rhodium-catalyzed nondecarbonylative addition reaction of ClCOCOOC2H5 to alkynes. Chemistry. 2005 Jun 6;11(12):3621-30.
Addition of ethoxalyl chloride (ClCOCOOEt) to terminal alkynes at 60 degrees C in the presence of a rhodium (I)-phosphine complex catalyst chosen from a wide range affords 4-chloro-2-oxo-3-alkenoates regio- and stereoselectively. Functional groups such as chloro, cyano, alkoxy, siloxy, and hydroxy are tolerated. The oxidative addition of ethoxalyl chloride to [RhCl (CO)(PR (3))(2)] proceeds readily at 60 degrees C or room temperature and gives [RhCl (2)(COCOOEt)(CO)(PR (3))(2)] (PR (3) = PPh (2) Me, PPhMe (2), PMe (3)) complexes in high yields. The structure of [RhCl (2)(COCOOEt)(CO)(PPh (2) Me)(2)] was confirmed by X-ray crystallography. Thermolysis of these ethoxalyl complexes has revealed that those ligated by more electron-donating phosphines are fairly stable against decarbonylation and reductive elimination. [RhCl (2)(COCOOEt)(CO)(PPh (2) Me)(2)] reacts with 1-octyne at 60 degrees C to form ethyl 4-chloro-2-oxo-3-decenoate. The catalysis is therefore proposed to proceed by oxidative addition of ethoxalyl chloride, insertion of an alkyne into the Cl--Rh bond of the resulting intermediate, and reductive elimination of alkenyl-COCOOEt. |
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