Synthesis of Oxacyclic Scaffolds via Dual Ruthenium Hydride/Brønsted Acid‐Catalyzed Isomerization/Cyclization of Allylic Ethers

A ruthenium hydride/Brønsted acid‐catalyzed tandem sequence is reported for the synthesis of 1,3,4,9‐tetrahydropyrano[3,4‐b]indoles (THPIs) and related oxacyclic scaffolds. The process was designed on the premise that readily available allylic ethers would undergo sequential isomerization, first to enol ethers (Ru catalysis), then to oxocarbenium ions (Brønsted acid catalysis) amenable to endo cyclization with tethered nucleophiles. This methodology provides not only an attractive alternative to the traditional oxa‐Pictet–Spengler reaction for the synthesis of THPIs, but also convenient access to THPI congeners and other important oxacycles such as acetals.     

Intermixed Adatom and Surface‐Bound Adsorbates in Regular Self‐Assembled Monolayers of Racemic 2‐Butanethiol on Au(111)

In situ scanning tunneling microscopy combined with density functional theory molecular dynamics simulations reveal a complex structure for the self‐assembled monolayer (SAM) of racemic 2‐butanethiol on Au(111) in aqueous solution. Six adsorbate molecules occupy a (10×√3)R30° cell organized as two RSAuSR adatom‐bound motifs plus two RS species bound directly to face‐centered‐cubic and hexagonally close‐packed sites. This is the first time that these competing head‐group arrangements have been observed in the same ordered SAM. Such unusual packing is favored as it facilitates SAMs with anomalously high coverage (30 %), much larger than that for enantiomerically resolved 2‐butanethiol or secondary‐branched butanethiol (25 %) and near that for linear‐chain 1‐butanethiol (33 %).     

Synthesis of tetrahydro-β-carbolines via isomerization of N-allyltryptamines: a metal-catalyzed variation on the Pictet-Spengler theme

An efficient and broadly applicable alternative to the classical Pictet-Spengler synthesis of tetrahydro-β-carbolines is presented. The method relies on metal-catalyzed isomerization of allylic amines to form reactive iminium intermediates which can be trapped by a tethered indole nucleophile.