title: Rhodium-catalyzed nondecarbonylative addition reaction of ClCOCOOC2H5 to alkynes.
abstract: 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.
authors.affiliation: Department of Chemistry, Tsinghua University, Beijing, P. R. China.
authors.forename: Ruimao
authors.initials: R
authors.lastname: Hua
authors.forename: Shun-Ya
authors.initials: SY
authors.lastname: Onozawa
authors.forename: Masato
authors.initials: M
authors.lastname: Tanaka
mesh_terms: D000480:Alkynes / Q000138:chemical synthesis / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D004952:Esters / Q000737:chemistry*; D006843:Hydrocarbons, Chlorinated / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012238:Rhodium / Q000737:chemistry*
chemical_list: D000480:Alkynes; D004952:Esters; D006843:Hydrocarbons, Chlorinated; D009942:Organometallic Compounds; C506859:ethoxalyl chloride; D012238:Rhodium