Stereochemical Control by an Ester Group or Olefin Ligand in Platinum‐Catalyzed Carboalkoxylation of 6‐(1‐Alkoxyethoxy)‐ hex‐2‐ynoates

Abstract

The cyclization of 6-(1-alkoxyethoxy)hex-2-ynoantes in the presence of the platinum-olefin catalyst system gave the corresponding multisubstituted 2-[dihydrofuran-2(3H)-ylidene]acetates in good to high yields. The Z/E selectivity is controlled by the electronic property of the ester group; the 2,2,2-trichloroethyl ester yielded the Z isomer, while the phenyl ester gave the E isomer. Moreover, we found that the Z/E selectivities in the reaction of phenyl esters 1h, 1n, and 1o were controlled by the olefin ligand. For example, the platinum-catalyzed reaction of 1h using 1,5-hexadiene as the olefin ligand gave E-2h as the major product, while that using 1,5-cyclooctadiene produced mainly the Z isomer.

Cationic Gold(I)-Catalyzed Cascade Bicyclizations for Divergent Synthesis of (Spiro)polyheterocycles

“…In this regard, the intramolecular addition of various nucleophiles, such as alcohols, thiols, and amines, to transition metal-activated alkynes has served as a powerful tool for constructing innumerable heterocycles in an efficient and atom-economic manner (Scheme a, R 2 = H) . Meanwhile, employing weaker nucleophiles, such as ethers, sulfides, tertiary amines, and amides, has resulted in the formation of heterocycles containing a disubstituted alkene in a single operation through rearrangement of the allyl, propargyl, acyl, α-alkoxy alkyl, sulfonyl, silane, or benzyl group (Scheme a, R 2 ≠ H). Furthermore, various fragment migrations have been involved as the key step in many homogeneous gold-catalyzed cascade processes for the effective synthesis of highly complex heterocycles and natural products .…”

π-Acid Mediated Insertion of Alkynes into Carbon–Heteroatom σ-Bonds

“…Influence of the olefin ligand on E/Z-selectivity for acetal migration Intriguingly, the stereochemical outcome with these substrates was also influenced by the choice of olefin additive (Scheme 26): the use of 1,5-hexadiene gave rise to near complete E-selectivity from 118, whilst the use of cyclooctadiene favoured formation of the Z-isomer 119. 39 Very recently, an intermolecular variant of this transformation has been reported. The gold-catalysed reaction between terminal alkyne 120 and dimethyl acetal 121 represents the first intermolecular example of such a process with a formal C-O addition across the alkyne and subsequent hydrolysis of the enol ether to afford the ketone 122 (Scheme 27).…”

Heteroatom methods

“…Stereoselectivity was somewhat variable and depended on both ligand and substrate, but some highly selective cases were observed (Scheme 8). 33…”