Analyze this! Residual dipolar couplings (RDCs) can be used to determine the constitution of a small molecule when traditional methods for structure elucidation fail. In a case study, a highly congested, tricyclic compound resulting from the electrophilic cyclization of an azide‐containing 1,5‐enyne was investigated.

This brief overview highlights recent progress in the field of cascade reactions that are initiated by the activation of a pi-system using platinum and gold catalysts and that are coupled with a 1,2-alkyl migration step. While the reactions discussed aim to rapidly evolve molecular complexity, they are experimentally straightforward and easy to perform. Primarily guided by the type of 1,2-alkyl migration, methods are categorized as shifts to metal carbenoid centers and pinacol-type rearrangements.

A combination of gold(I) complexes and amine bases catalyzes the 5-exo-dig cyclization of formyl alkynes. This direct alpha-functionalization of aldehydes with unactivated alkynes does not involve the use of preformed enol equivalents.

Au‐spicious! Under silver‐free conditions, simple 3‐silyloxy‐1,5‐enynes were converted into complex cyclopentenes by a gold(I)‐catalyzed sequence that likely proceeds through a carbocyclization followed by a pinacol rearrangement. For the final demetalation step, isopropyl alcohol and N‐iodosuccinimide are effectively utilized, and the resulting products are set up for a wealth of further reactions.

Two protocols for the construction of 4-iodo-3-furanones through a sequence consisting of cyclization and 1,2-migration of 2-alkynyl-2-silyloxy carbonyl compounds were developed. In one, electrophilic cyclization is directly induced by N-iodosuccinimide (NIS). In the second less limited variant, AuCl3 catalyzes the tandem reaction in the presence of NIS to provide highly substituted heterocycles in moderate to excellent yields.

Valuable six‐membered carbocycles including highly substituted benzenes, 1,4‐cyclohexadienes, and 4‐fluorocyclohexenes can be prepared from simple 1,5‐enynes by iodonium‐induced cyclization. This cyclization strategy was applied to the total synthesis of cybrodol, a sesquiterpenoid with a pentasubstituted aromatic core (see scheme).

Two platinum(II)-catalyzed heterocyclization-migration reactions that provide five-membered heterocycle products are described. With 5 mol-% of PtCl 2 as a catalyst, 2-alkynyl-2-hydroxy carbonyl compounds 1 are converted into 3(2H)-furanones 2 at 80°C in moderate to excellent yields under very mild reaction conditions. The reaction is proposed to proceed through an oxonium ion intermediate B, which triggers a stereospecific 1,2-shift analogous to an α-ketol rearrangement. When exploited in a different manner, the 2-alkynyl-2-hydroxy carbonyl compounds 1 afford 3-pyrrolones 3 in 33-81 % yield. For this purpose, the starting compounds 1 are

o-Iodoxybenzoic acid (IBX) was found to mediate the conversion of alpha-alkynyl alcohols into Z-enediones under notably mild conditions via a novel rearrangement mechanism (33-65% yield, 13 examples).