A Fischer-Type Ruthenium Carbene Complex as a Metathesis Catalyst for the Synthesis of Enol Ethers

Abstract

The Grubbs G-I or G-II catalyst gives the ruthenium ethoxy carbene complex, which catalyzes ring-opening cross metathesis (ROCM) of a strained cyclic alkene to give a diene where one of the two alkene moieties in the product contains an ethoxy substituent. No polymeric products are detected. Hydrocarbons such as parent norbornene or substituted cyclopropenes can proceed with the reaction smoothly. Tertiary amines, N-alkylimides, esters, and aryl or alkyl bromides remain intact under the reaction conditions. In addition to vinyl ethers, vinylic esters can also be used. The time required to reach a 50% yield of the ROCM product t 50 varies from 0.01 to 140 h depending on the strain and nucleophilicity of the double bond. Anchimeric participation of an electron-rich group would result in significant enhancement of the reactivity, and the t 50 could be as short as several minutes. A similar substrate without such a neighboring group shows a much slower rate. An exo-norborne derivative reacts much faster than the corresponding endo-isomer. Alkenes with poor nucleophilicity are less favored for the ROCM process, so is less strained cyclooctene.

A tribute to Professor Tien-Yau Luh

“…A systematic study on the relative reactivity for the ring opening cross metathesis of different strained cycloalkenes with a large excess of EVE for the synthesis of electron rich alkenes is shown in Figure 8. 96 The t50 is defined as the time required for the consumption of 50% of the starting material.…”

Self‐Assembly and In Situ Quaternization of Triblock Bottlebrush Block Copolymers via Organized Spontaneous Emulsification for Effective Loading of DNA

“…Norbornene-terminated polystyrene (NB-PS) and norborneneterminated polyethylene oxide (NB-PEO) macromonomers as well as the norbornene-terminated bromoethane (NB-Br) monomer was synthesized according to reported procedures (see Scheme S1 and Figure S1, Supporting Information). [43][44][45][46] The synthesis of triblock BBCPs was achieved through sequential ring-opening metathesis polymerization (ROMP) using the third generation Grubbs catalyst (see Scheme S2, Supporting Information). [42,47,48] The NB-PS monomer was first polymerized initiated by adding the Grubbs catalyst.…”