Rhodium-Catalyzed Reductive Cyclization of 1,6-Diynes and 1,6-Enynes Mediated by Hydrogen:  Catalytic C−C Bond Formation via Capture of Hydrogenation Intermediates

• Published in: Journal of the American Chemical Society Vol. 126; no. 25; pp. 7875 - 7880
• Main Authors: Jang, Hye-Young, Krische, Michael J
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 30.06.2004; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; Organic chemistry; Physical Sciences; Science & Technology; ASYMMETRIC CATALYSIS; OPPORTUNITIES NOBEL LECTURE; SELECTIVE HYDROGENATION; SILYLATIVE CYCLIZATION; FORMING HYDROGENATION; CYCLOISOMERIZATION; FISCHER-TROPSCH SYNTHESIS; STEREOSELECTIVE HYDROFORMYLATION; ENYNE COMPOUND; DIYNES; Catalytic reaction; Cyclization; Rhodium Complexes; Regioselectivity; Platinoid Complexes; Transition metal Complexes; Complex catalyst; Diynic compound; Experimental study; Catalyst activity; Hydrogenation; Enynic compound
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja048498i

Catalytic hydrogenation of carbon-, nitrogen- and oxygen-tethered 1,6-diynes 1a−9a and 1,6-enynes 10a−18a using cationic Rh(I) precatalysts at ambient temperature and pressure enables reductive carbocyclization to afford 1,2-dialkylidene cyclopentanes 1b−9b and monoalkylidene cyclopentanes 10b−18b, respectively, in good to excellent yields and as single alkene stereoisomers. Notably, the 1,3-diene and alkene containing cyclization products 1b−9b and 10b−18b are not subject to over-reduction under the conditions of catalytic hydrogenation in which they are formed. Reductive cyclization 1,6-diyne 1a and 1,6-enyne 10a performed under an atmosphere of D2 provides the carbocyclization products deuterio-1b and deuterio-10b, respectively, which incorporate two deuterium atoms. The collective data are consistent with a catalytic mechanism involving heterolytic activation of elemental hydrogen (H2 + Rh+X- → Rh−H + HX) followed by Rh(I)-mediated oxidative cyclization of the 1,6-diyne or 1,6-enyne substrates to afford (hydrido)Rh(III)-based metallocyclopentadiene and metallocyclopentene intermediates, respectively. These transformations represent the first examples of metal-catalyzed reductive carbocyclization mediated by hydrogen.