Synthesis of Fulvene Vinyl Ethers by Gold Catalysis

Abstract

Gold-catalyzed cyclization of 1,5-diynesw ith ketones as reagents and solvent provides diversely substituted vinyl ethers under mild conditions. The regioselectivity of such gold-catalyzed cyclizations is usually controlled by the scaffold of the diyne. Herein, we report the first solvent-controlled switchingo fr egioselectivity from a6 -endo-dig-to 5endo-dig-cyclization in these transformations,p roviding fulvene derivatives. With respectt ot he functional-group toler-ance, aryl fluorides, chlorides, bromides,and ethers are tolerated. Furthermore, the mechanism and selectivity are put to scrutinyb ye xperimental studies and at hermodynamic analysis of the product. Additionally,6 -(vinyloxy)fulvenesa re a hitherto unknown class of compounds. Theirr eactivity is briefly evaluated, to give insights into their potential applications.[ + + ] Crystallographic investigation;T heoreticali nvestigation Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Copper-catalyzed enantioselective diyne cyclizationviaC(sp2)–O bond cleavage

“…(b) Free energy profile for the synthesis of chromeno [3,4-c]pyrrole (+)-2a from diyne substrate 1a. Relative free energies (DG, in kJ mol −1 ) of all the transition states and intermediates were computed at the SMD(PhCF 3 )-M06/6-31G(d,p) &LANL2DZ level of theory, with the electronic energy of all the transition states and intermediates recomputed at the SMD(PhCF (DFT) calculations (for more details see the ESI †), a plausible mechanism involving vinyl cation intermediates 11 for the formation of chiral chromeno [3,4-c]pyrrole (+)-2a from diyne 1a is displayed in Scheme 3. The Cu I catalyst rst preferentially coordinates to the electron-richer amide-tethered C^C bond of 1a to form precursor A, followed by intramolecular trapping by the N-propargyl moiety, affording the vinyl cation intermediate B.…”

“…9 However, successful examples of asymmetric catalysis based on vinyl cation intermediates have been scarcely reported. Very recently, we have developed a facile copper-catalyzed diyne cyclization for the generation of vinyl cations, 10,11 and achieved a series of asymmetric reactions by this strategy via a remote control of enantioselectivity, including intramolecular aromatic C(sp 2 )-H functionalization, 10e vinylic C(sp 2 )-H functionalization, 10c cyclopropanation, 10e [1,2]-Stevens-type rearrangement 10b and intermolecular annulations with styrenes 10d and ketones. 10a Inspired by the above results and by our recent study on developing ynamide chemistry for heterocycle synthesis, 12,13 we envisioned that replacing the benzyl group with an aryl group may lead to C(sp 2 )-O bond cleavage by employing this asymmetric copper catalysis.…”

Optimizing Catalyst and Reaction Conditions in Gold(I) Catalysis–Ligand Development

“…119 [Au(IPr*)(NCCH 3 )]SbF 6 showed also a higher catalytic activity than the corresponding IPr-gold analogues in the cyclization of 1,5-diynes with ketones to afford fulvene vinyl ethers (Scheme 49). 120 [Au(NHC)(NEt 3 )][HF 2 ] complexes catalyzed the hydrofluorination of diphenylacetylene with NEt 3 •3HF. 108 The 108 In agreement with an earlier report by Sadighi and coworkers, among the three IPr-based species, the less electron-rich carbene, IPr Cl , gave the higher reaction yield (Scheme 44, section 3.1.1.1).…”

Gold Catalysis: 2,3‐ or 1,4‐Addition to Butadiynes

“…In contrast to this observation, here we present the first gold‐catalyzed intermolecular functionalization of 1,3‐butadiynes by two nucleophiles to selectively give 1,3‐butadienes. Since the two‐fold addition of alcohols to mono‐alkynes is the common mode of reactivity observed, [43–44] this opens up a facile synthetic route to di(vinyl ethers), which are usually challenging to synthesize by gold catalysis [45–49] …”