Gold‐Promoted Sigmatropic Rearrangements

Abstract

Gold catalysis is particularly efficient in mediating various kinds of sigmatropic rearrangements that either correspond to an overall transformation of a substrate or simply occur as an elementary step in a reaction sequence. Among the sigmatropic rearrangements that can be gold‐promoted, particular attention has been brought to the Cope and Claisen rearrangements, and to the rearrangement of propargylic esters, which have been the subject of numerous experimental and theoretical investigations. Compared to the thermally induced version of such rearrangements, the use of electrophilic gold species as catalysts allows significant reduction in the energy demand so that transformations can generally be performed at moderate temperature with a good control of the chemo‐ and/or stereoselectivities. This chapter gives an overview of the various synthetic methods based on the use of gold‐promoted sigmatropic rearrangements that have been reported so far.

The Outer‐Sphere Mechanism of Nitrene Transfer onto Gold(I) Alkyne Complexes

“…This rearrangement is typical in carbenes with α‐hydrogen atoms but is uncommon in gold carbenes. Notable exceptions that have been reported include a study by Gevorgyan on 1,2‐H and 1,2‐Si migrations onto gold carbenes in 2 H ‐furan‐3‐gold carbene intermediates assisted by rearomatization at the furan ring and the 1,2‐H migrations proposed in the gold‐catalyzed intramolecular acetylenic Schmidt reaction . The atomic motion in this step resembles that of a type I dyotropic rearrangement involving both the α‐H and gold atoms.…”

“…Notable exceptionst hat have been reported include as tudy by Gevorgyan on 1,2-H and 1,2-Si migrations onto gold carbenes in 2H-furan-3-gold carbene intermediates assistedb yr earomatization at the furan ring [47] and the 1,2-H migrations proposed in the gold-catalyzed intramolecular acetylenic Schmidt reaction. [30,[48][49][50] The atomic motion in this step resembles that of at ype Idyotropic rearrangement [51] involving both the a-H and gold atoms. In this kind of rearrangement, two concerted 1,2-shifts of substituents attachedt oa djacent carbon atoms occur,s ot hat they exchange their relative positions.…”

Rh(II)-Catalyzed Enynal Cycloisomerization for the Generation of Vinyl Carbene: Divergent Access to Polycyclic Heterocycles

“…Vinyl metal carbenes, a crucial type of functionalized metal carbenes, have wide applications in organic synthesis for their diversified transformation sites, thus offering a rapid route to a wide range of functionalized products . However, examples with alkynes as vinyl metal carbene precursors are much less reported (Scheme a, right). − The easily accessible propargylic esters and propargylic thioether were the dominating reported precursors. , Among them, the propargylic esters were usually activated by carbophilic metal complexes, such as gold­(I), rhodium­(I), etc., followed by 1,2-migration of the acyloxy of propargylic esters for the formation of vinyl carbene, which usually presents a noncyclic structure . Besides, 1,2-acyloxy migration is usually limited to substrates derived from tertiary or benzylic alcohols containing terminal alkynes, thus to a significant extent limiting their synthetic utilities .…”