Gold Catalysis: Domino Reaction of En‐Diynes to Highly Substituted Phenols

Abstract

By Sonogashira coupling of 1,7-heptadiynes and 1,8-octadiynes with 2-iodoallyl alcohols, various substrates that bear a 2-alkynylallyl alcohol moiety tethered to an additional alkyne were prepared in one step. Subjection to nitrogen acyclic carbene (NAC)/gold(I) catalysts delivered highly substituted phenols in an efficient domino reaction. Furan derivatives were formed as intermediates; this was proven by in situ NMR spectroscopy. The uncommon substitution pattern of these furans opens the way for a selective formation of phenols that contain the hydroxyl group in the meta position to the ring junction, which previously was not possible by gold-catalyzed furan-yne cyclization. Furthermore, interesting mechanistic insights were obtained by products derived from secondary allyl alcohols. In this case, in addition to the phenolic compounds, a ketone is formed by 1,2-alkyl shift.

Synthesis of 1,2,3-triazole-linked galactohybrids and their inhibitory activities on galectins

“…The obtained dimeric structures are characterized by an extended bis(1,2,3-triazol-4-yl)linker. The linear alkadiynes (entries 1-4, Table 1) are commercially available, but other precursors of the linkers (1,2-bis(propargyloxy)ethane, 25 2,2-dipropargyl dimedone (4a), 26 5,5-dipropargyl Meldrum's acid (4b) 27 and 5,5-dipropargyl barbituric acid (5) 25 6a-e (see Table 1 Similarly, a combination of 1,3,5-triethynylbenzene (7) and penta-O-propargyl-β-D-glucose (9) 28 with a minimal excess of azidosugar 2 gave trivalent and pentavalent galacto-clusters 8 and 10 in 74 and 61% yields, respectively (Scheme 2).…”

When NHC Ligands Make a Difference in Gold Catalysis

“…Acyclic diaminocarbenes (ADCs), also known as NACs, have more recently emerged as a very valuable family of ligands, complementary to NHCs 16. An illustration of this has been given by Hashmi in a versatile synthesis of phenols (Scheme ) 17…”

Gold‐Catalyzed Cascade Reactions of Alkynes for Construction of Polycyclic Compounds

“…In a related reaction, the Hashmi group reported a gold‐catalyzed cascade cyclization of diyne‐substituted allylic alcohols 150 for regioselective synthesis of highly substituted phenols 151 (Scheme ) 43. The reaction of 150 with a (NAC)‐gold(I) complex gives the furan‐yne intermediates 152 that bear an alkynyl substituent at the 2‐position.…”