Synthesis of δ- and ε-Cyanoesters by Zinc-Catalyzed Ring-Opening of Cyclic Ethers with Acid Chlorides and Subsequent Cyanation

Abstract

In the present study, the zinc-catalyzed cleavage of cyclic ethers with acid halides as nucleophiles to yield chloroesters with different chain length has been investigated in detail. In the presence of straightforward and commercially available zinc salts as pre-catalysts excellent yields and selectivities were feasible. After studying the reaction conditions and the scope of the method, several efforts were carried out to understand the reaction mechanism. The obtained chloroesters were subsequently converted to d-and e-cyano esters, which are useful precursors in natural product synthesis.

Hexafluoro-2-propanol-Promoted Intermolecular Friedel–Crafts Acylation Reaction

“…2 equiv needed in the intramolecular reactions). As previously observed, H-bond accepting solvents THF and acetonitrile had strongly inhibiting effects; in the former case, 4-chlorobutyl benzoate resulting from THF cleavage was also obtained (entries 5 and 6) …”

Rise of the Zinc Age in Homogeneous Catalysis?

“…108−110 More recently, Enthaler and co-workers have set up for the first time a capable protocol for the depolymerization of polyethers with acid chlorides in the presence of catalytic amounts of abundant and cheap zinc salts to yield chloroesters as defined products (Scheme 6f). 111,112 Remarkably, the chloroesters were obtained at comparable mild reaction conditions and can be useful synthons in polymerization chemistry to prepare new polymers. Overall a recycling of polymers is feasible.…”

“…Moreover, the zinc catalyzed reduction of a variety of sulfoxides with silanes or boranes as reductant to the corresponding sulfide has been examined by the group of Enthaler. With the straightforward and commercially available zinc­(II) triflate as the precatalyst, excellent yields and chemoselectivities for a broad variety of substrates were realized (Scheme e). − More recently, Enthaler and co-workers have set up for the first time a capable protocol for the depolymerization of polyethers with acid chlorides in the presence of catalytic amounts of abundant and cheap zinc salts to yield chloroesters as defined products (Scheme f). , Remarkably, the chloroesters were obtained at comparable mild reaction conditions and can be useful synthons in polymerization chemistry to prepare new polymers. Overall a recycling of polymers is feasible.…”

Mutual Cooperation in the Formal Allyl Alcohol Nucleophilic Substitution and Hydration of Alkynes for the Construction of γ‐Substituted Ketones

“…[10, 14a, b] With the assistance of Lewis acid Au I or Au III salt, the CÀOb ond at the allylic position is cleaved, and simultaneously the ring-opening of Int-6 a occurred and gave the allyl cation intermediate TS-4.T ot he best of our knowledge,t his type of ring-opening of the vinyl tetrahydrofuran was unprecedented. [15,16] The external alcohol as an ucleophile attacked the allyl cation to complete the S N 1a llylic alkoxylation and resulted in the only thermodynamically stable g-methoxylketone. Herein, the gold catalyst acts as both p-acid to accelerate the OÀHi nsertion into the triple bond and Lewis acid to mediate allylic ether CÀOb ond cleavage.…”