Transition metal-catalyzed acyloxy migration of propargylic esters offers versatile entries to allene and vinyl carbene intermediates for various fascinating subsequent transformations. Most π-acidic metals (e.g. gold and platinum) are capable of facilitating these acyloxy migration events. However, very few of these processes involve redox chemistry, which are well-known for most other transition metals such as rhodium. The coupling of acyloxy migration of propargylic esters with oxidative addition, migratory insertion, and reductive elimination may lead to ample new opportunities for the design of new reactions. This tutorial review summarizes recent developments in Rh-catalyzed 1,3- and 1,2-acyloxy migration of propargylic esters in a number of cycloaddition reactions. Related Au- and Pt-catalyzed cycloadditions involving acyloxy migration are also discussed.

A new type of rhodium-catalyzed [5+2] cycloaddition was developed for the synthesis of seven-membered rings with diverse functionalities. The ring formation was accompanied by a 1,2-acyloxy migration event. The 5- and 2-carbon components of the cycloaddition are 3-acyloxy-1,4-enynes (ACEs) and alkynes respectively. Cationic rhodium (I) catalysts worked most efficiently for the intramolecular cycloaddition, while only neutral rhodium (I) complexes could facilitate the intermolecular reaction. In both cases, electron-poor phosphite or phosphine ligands often improved the efficiency of the cycloadditions. The scope of ACEs and alkynes was investigated in both intra- and intermolecular reactions. The resulting seven-membered ring products have three double bonds that could be selectively functionalized.

A highly chemoselective, regioselective, and stereospecific synthesis of polysubstituted cyclobutenes, by catalyst‐controlled ring expansion of cyclopropanes via metal carbene intermediates, is reported. Transition‐metal catalysts showed profound effects on the reactivity and selectivity of metal carbene intermediates in this ring‐expansion reaction.

Lead Rh‐ole: Highly substituted cyclohexenones were prepared from cyclopropyl‐substituted propargyl esters by using a [{Rh(CO)2Cl}2] catalyst. This metal catalyst promoted the 1,3‐acyloxy migration of propargyl esters and a subsequent [5+1] cycloaddition of the resulting allenylcyclopropanes in the presence of CO with high regioselectivity.

Rholling in the bicycles: A rhodium(I)‐catalyzed cycloisomerization for the synthesis of bicyclic compounds containing a cycloheptatriene ring from linear alkenynes (see scheme; cod=1,5‐cyclooctadiene) is proposed to proceed through 1,2‐acyloxy migration, 6 π electrocyclization, migratory insertion, and reductive elimination. The overall process can be viewed as a novel intramolecular [5+2] cycloaddition with concomitant 1,2‐acyloxy migration.