Jang Hye-Young, Krische Michael J
University of Texas at Austin, Department of Chemistry and Biochemistry, Austin, Texas 78712, USA.
J Am Chem Soc. 2004 Jun 30;126(25):7875-80. 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 D(2) 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 (H(2) + 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.
在室温和常压下，使用阳离子铑（I）预催化剂对碳、氮和氧连接的1,6 - 二炔1a - 9a和1,6 - 烯炔10a - 18a进行催化氢化，能够实现还原碳环化反应，分别以良好至优异的产率得到1,2 - 二亚烷基环戊烷1b - 9b和单亚烷基环戊烷10b - 18b，且产物为单一烯烃立体异构体。值得注意的是，含有1,3 - 二烯和烯烃的环化产物1b - 9b和10b - 18b在其形成的催化氢化条件下不会过度还原。在D₂气氛下对1,6 - 二炔1a和1,6 - 烯炔10a进行还原环化反应，分别得到含有两个氘原子的碳环化产物氘代 - 1b和氘代 - 10b。这些总体数据与一种催化机理一致，该机理涉及元素氢的异裂活化（H₂ + Rh⁺X⁻ → Rh - H + HX），随后铑（I）介导1,6 - 二炔或1,6 - 烯炔底物进行氧化环化反应，分别生成基于（氢化）铑（III）的金属环戊二烯和金属环戊烯中间体。这些转化代表了由氢介导的金属催化还原碳环化反应的首例。
