Rhodium-catalyzed nondecarbonylative addition reaction of ClCOCOOC2H5 to alkynes

Addition of ethoxatyl chloride (CICOCOOEt) to terminal alkynes at 60 degrees C in the presence of a rhodium(i)-phosphine complex catalyst chosen from a wide range affords 4-choro-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)(PR2)(2)] proceeds readily at 60 degrees C or room temperature and gives [RhCl2(COCOOEt)(CO)(PR3)(2)] (PR3 = Pph(2)Me, PPhMe2, PMe3) Complexes in high yields. The structure of [RhCl2(COCOOEt)(CO)(PPh2Me)(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. [RhCl2(COCOOEt)(CO)(PPh2Me)(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.