Stereoselective Gold(I)‐Catalyzed Vinylcyclopropanation via Generation of a Sulfur‐Substituted Vinyl Carbene Equivalent

Abstract

A stereoselective gold(I)‐catalyzed vinylcyclopropanation of alkenes has been developed. A gold‐coordinated cationic vinyl carbene species, readily generated via a rearrangement of the ethylenedithioacetal of propargyl aldehyde, reacts with a wide range of alkenes to afford thio‐substituted vinylcyclopropanes. The gold‐catalyzed vinyl cyclopropanation proceeds under mild conditions at room temperature and is generally selective for the formation of cis‐substituted cyclopropanes. The reaction allows the formal introduction of a “naked” vinyl carbene, by subsequent chemoselective hydrodesulfurisation of the ethylenedithio‐bridge. The synthetic utility of the new method is demonstrated by a short, racemic formal synthesis of the alkaloid cephalotaxin, hinging on a key vinyl cyclopropane‐cyclopentene rearrangement.

Dearomative [4 + 3] cycloaddition of furans with vinyl-N-triftosylhydrazones by silver catalysis: stereoselective access to oxa-bridged seven-membered bicycles

“…This achievement clearly demonstrated the superiority of current method, as unsubstituted vinyl carbenes underwent self-condensation more easily than the substituted ones. 22,23 Overall, the results summarized in Schemes 1 and 2 clearly demonstrated the superior features of silver-catalyzed [4 + 3] cycloaddition between furans and vinyl- N -triftosylhydrazones, namely the broad substrate scope, good functional group tolerance, excellent chemo-, regio- and endo -stereoselectivity, and good to high yield, thereby constituting a versatile method for the stereoselective synthesis of a wide range of endo oxa-bridged 1,4-cycloheptadienes.…”

Gold‐Catalyzed Reactions of 2‐Alkynyl‐1‐indolyl‐1,2‐diols with Thiols: Stereoselective Synthesis of (Z)‐α‐Indol‐3‐yl α‐(2‐Thioalkenyl) Ketones

“…[5] Other 1,2-and 1,3sulfur shifts have been reported, [6] and more recently the intermolecular cyclopropanation reaction of these sulfur-substituted gold vinylcarbenoids has also been described. [7] Following our interest in the development of goldcatalyzed reactions involving the functionalization of indoles, [8] we have reported the synthesis of 1-(indol-3yl)carbazoles from readily available α-bis(indol-3-yl) methyl alkynols through an unexpected and selective 1,2-migration of the indolylmethyl vs. the alkenyl group, which has also been supported by DFT calculations (Scheme 1b, eq. 3).…”