Mercury(II) Triflate-Catalyzed Cycloisomerization of Allenynes to Allenenes

Abstract

Cycloisomerizations of allenynes to allenenes have been studied in the presence of catalytic amounts of [Hg(OTf)2] in acetonitrile. The catalytic system is quite effective for terminal 1,6-allenynes: allenenes were obtained in reasonable to high yields. However, treatment of allenynes with disubstituents at the allenic terminal carbon yielded a triene and/or allenene as a major product(s) depending upon the substituents.

Hg(OTf)2-Catalyzed Arylene Cyclization

“…We propose that the reaction is likely to be initiated from a π-complex 9 . , Friedel−Crafts type cyclization leads to carbocation 10 , and the organomercuric intermediate 11 is produced by deprotonation. Protonation of the hydroxyl moiety of 11 by in situ generated TfOH leads to oxonium cation 12 .…”

“…The reaction involves protonation of the alkenyl mercury intermediate 3 with in situ formed TfOH to generate cation 4 . Subsequent smooth demercuration leads to 2 and the regenerated catalyst. , Hg(OTf) 2 was originally developed in 1983 as an efficient olefin cyclization agent, and the reaction of farnesyl sulfone 5 with 1.2 equiv of Hg(OTf) 2 •PhNMe 2 afforded bicyclic product 6 in 74% yield . Because the latter reaction produces stable organomercuric product 6 , it is essentially a stoichiometric reaction .…”

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

“…In a Hg(OTf) 2 -catalyzed process, 1,6-allenynes 158 were cycloisomerized to generate allenenes 159 in moderate to good yield ( Scheme 46 ) [ 105 ]. However, depending on the substituents, allenene and/or unexpected triene were produced as a main product for disubstituted 1,6-allenynes.…”

“…The stereochemistry of the chiral amino acid was not conserved in the cyclized product hence it leads to the formation of racemic products with moderate yields (Scheme 44). In a Hg(OTf) 2 -catalyzed process, 1,6-allenynes 158 were cycloisomerized to generate allenenes 159 in moderate to good yield (Scheme 46) [105]. However, depending on the substituents, allenene and/or unexpected triene were produced as a main product for disubstituted 1,6-allenynes.…”

Copper-catalyzed remote double functionalization of allenynes

“…We initiated the study with the reaction of allenyne 1a 70–89 and B 2 (pin) 2 2a in the presence of MeOH with NaO t Bu as the base and CuCl (5 mol%) and Biphep ( L 1 ) (6 mol%) as the catalyst at 30 °C in THF for 16 h. To our delight, the 2,5-addition product, 1,3,4-trienyl boronate 3aa , was formed in 33% yield with 3% yield of the 2,3-addition product, 1,4-enyne 3aa′ (entry 1, Table 1). Upon adjusting the ratio of 1a / 2a to 1/1, a much higher yield of the desired product 3aa was achieved (entries 2–5, Table 1).…”