Gold(I)‐Catalyzed Domino Reaction of Allyl 2‐en‐4‐ynyl Ethers to 1,3,6‐Trien‐4‐yl Ketones

Abstract

The gold(I)‐catalyzed reaction of allyl 2‐en‐4‐ynyl ethers provides stereoselectively (Z)‐1,3,6‐trienes with an acyl substitutent in the 4‐position. The reaction proceeds through an oxygen transfer along the chain and a clean allylic inversion. This complements the preceding work by Gagosz, who obtained furan derivatives in his investigation of similar substrates with terminal alkynyl groups.10, 16 The only drawback of this mechanistically new pathway is the instability of the products under the reaction conditions, which sometimes prevents their isolation in high yields.

Regio‐ and Site‐selective Molecular Rearrangements by Homogeneous Gold Catalysis

“…[241] Under identical conditions, substrate lacking aromatic backbone such as allyl 2-en-4-ynyl ethers undergo the Au(I)catalyzed 6-endo-dig cyclization/ [3,3]-σ-tropic rearrangement/ electrocyclic ring-opening sequence to generate open chain 1,3,6-trien-4-yl ketones. [242] In another occurrence, the Au(I)catalyzed conversion of related ynamide substrates 236 into substituted benzofurans 237 in an event of 5-endo-dig cyclization/rearrangement of oxonium intermediates is documented, although with diminished regioselectivity (Scheme 55). [243] In these examples, with an exception to ynamides possessing allyl ethers, those with crotyl or prenyl chain affords a mixture of regioisomeric benzofurans 238 and 239 in non-equivalent proportions signifying the functioning of both cationic as well as sigmatropic mechanism.…”

Gold(i)-catalyzed cycloisomerization of vinylidenecyclopropane-enes via carbene or non-carbene processes

“…Subsequent cyclopropanation produces polycyclic adduct 2a . When the ortho -position is substituted by a Me, Cl, Br or t Bu group, due to the increased nucleophilicity of the oxygen atom, 3g attacks the middle carbon of the allenyl moiety in intermediate D to give the corresponding oxonium intermediate E , which undergoes S′ E allyl-transfer 15 to afford product 4g via an intimate ion-pair F . In the case of 3k , the oxygen atom exclusively attacks the terminal carbon at the allene moiety of VDCP in intermediate G to give the corresponding oxonium intermediate H presumably due to the steric bulkiness at the alkene site, which similarly undergoes the allyl-transfer to give 5k via an intimate ion-pair I .…”

Gold(I)‐Catalyzed Intramolecular Cycloisomerization of Propargylic Esters with Furan Rings

“…We were pleased to find that 1 p – r gave much better results. Substituted furan 1 s also produced the corresponding α,β‐unsaturated methyl ketone15 2 s in 92 % yield as approximately 10:1 ( E / Z ) isomers. Substrates 1 t and 1 w bearing different substituents on the propargyl esters were also suitable for this reaction, giving the corresponding cyclized products as isomeric mixtures in reasonable yields.…”