No abstract

Gold forms rings: AuCl‐catalyzed cyclization of (α‐alkoxy alkyl) (ortho‐alkynyl phenyl) sulfides 1 proceeds under mild conditions to give 3‐(α‐alkoxy alkyl) benzothiophenes 2 in high yields for a wide range of substrates (see scheme). The starting materials are readily available through acetalization of ortho‐bromobenzenethiol and subsequent Sonogashira coupling. This methodology provides an atom‐economic route to sulfur‐containing heteroarenes.

The intramolecular aminoacylation of alkynes using ortho-alkynylacetanilides proceeds in very high yields in the presence of PtCl2 catalyst. This reaction provides not only a useful procedure for synthesizing 2,3-disubstituted indoles at once from ortho-alkynylaniline derivatives, but also an interesting mechanistic aspect; the intramolecular C-N bond addition of amides to alkynes takes place readily in the presence of Pt(II) catalyst.

Consecutive formation of CN and CS bonds: The gold‐catalyzed intramolecular aminosulfonylation of 2‐alkynyl‐N‐sulfonylanilines 1 (R1=H) produces 3‐sulfonylindoles 2 in good to high yields, whereas the indium‐catalyzed aminosulfonylation of 2‐alkynyl‐6‐methoxy‐N‐sulfonylanilines 1 (R1=MeO) affords 6‐sulfonylindoles 3 as the major products (see scheme).

The gold-catalyzed cyclization of (ortho-alkynylphenylthio)silanes 1 produced the corresponding 3-silylbenzo[b]thiophenes 2 in good to excellent yields. For example, the reaction of [2-(1-pentynyl)phenylthio]triisopropylsilane 1a, [2-(p-anisylethynyl)phenylthio]triisopropylsilane 1e, and [2-(phenylethynyl)phenylthio]triisopropylsilane 1g in the presence of 2 mol % of AuCl in toluene at 45 degrees C gave 2a, 2e, and 2g in 98, 99, and 97% yields, respectively. This reaction proceeds through intramolecular capture of the vinyl-Au intermediate by the silicon electrophile, so-called silyldemetalation.