Gold‐Catalyzed Double Cycloisomerization of 1‐Ene‐4,10‐diynyl Esters to Bicyclo[6.3.0]undeca‐2,4,9‐trienyl Esters

Abstract

A synthetic method to prepare bicyclo[6.3.0]undeca-2,4,9,trienyl esters efficiently from gold(I)-catalyzed Rautenstrauch rearrangement/1,5-hydride shift/8-endo-dig cyclization of 1-ene-4,10-diynyl esters is described. The suggested double cycloisomerization mechanism delineates the first example of an unactivated all-carbon tethered 1,7-enyne, either preformed or formed in situ, which undergoes an 8-endo-dig cyclization pathway to give a cyclooctane motif. It also offers an extremely rare synthetic method in organic chemistry that can sequentially assemble both ring components of the bicyclic motif from an acyclic precursor in one step.

Construction of Medium-Sized Rings by Gold Catalysis

“…Recently, Chan also demonstrated a methodology for construction of cyclopenta [8]annulene frameworks including compounds with a bicyclo[6.3.0]undecane skeleton. 157 Utilizing 1-ene-4,10-diynyl esters 142 as starting materials under gold catalysis, a double cycloisomerization provides an expedient strategy for construction of both ring components of bicyclic compounds 145, Scheme 37. Following the first alkyne activation by the gold catalyst, the remaining alkyne group in the putative cyclopentenyl gold complex 143 is believed to further coordinate with the Au catalyst to give the Au(I)-activated species 144, which is susceptible to a sequential 1,5-hydride shift/8-endo-dig cyclization reaction.…”

“…Recently, Chan also demonstrated a methodology for construction of cyclopenta[8]­annulene frameworks including compounds with a bicyclo[6.3.0]­undecane skeleton . Utilizing 1-ene-4,10-diynyl esters 142 as starting materials under gold catalysis, a double cycloisomerization provides an expedient strategy for construction of both ring components of bicyclic compounds 145 , Scheme .…”

Regio‐ and Site‐selective Molecular Rearrangements by Homogeneous Gold Catalysis

“…[121] 1-Ene-4,10-diynyl esters 27 are another series of reactants which undergoes cascade reaction initiated by 1,2-ester shift by Au(I)-catalysis. [122] In this substrate, the initially formed Au-cyclopentadienyl cation intermediate 28 undergoes a tandem 1,5-hydride shift/8-endo-dig cyclization with the aptly tethered long chain alkyne residue to form bicyclo [6.3.0]undeca-2,4,9,triene rings 29 (Scheme 8, eq 2). One report shown by Davies and Albrecht, highlighted the Au(I)catalyzed in situ generation of sulphur ylides from propargylic esters, wherein the rearrangement is initiated by a 1,2-ester shift.…”

“…This tandem reaction proceeds through a cascade 1,2‐acyl migration/Nazarov cyclization/Diels‐Alder intermediary 26 to afford 3 a ,6‐methanoisoindole esters 25 as single regio‐ and diastereoisomers [121] . 1‐Ene‐4,10‐diynyl esters 27 are another series of reactants which undergoes cascade reaction initiated by 1,2‐ester shift by Au(I)‐catalysis [122] . In this substrate, the initially formed Au‐cyclopentadienyl cation intermediate 28 undergoes a tandem 1,5‐hydride shift/8‐ endo ‐ dig cyclization with the aptly tethered long chain alkyne residue to form bicyclo[6.3.0]undeca‐2,4,9,triene rings 29 (Scheme 8, eq 2).…”

Rhodium(i)-catalysed cycloisomerisation/6π electrocyclisation of 5-(ethynylamino)pent-2-yn-1-yl esters to 2,3-dihydrobenzo[f]indoles

“…7 In the intervening years, this study has acted as the inspiration for the realisation of a myriad of elegant methods that utilise these two modes of reactivity to rapidly increase molecular complexity in a single step. 8–29 For instance, we recently described a convenient synthetic route to partially hydrogenated benzo[ g ]quinolines that relied on an initial gold( i )-catalysed cascade [3,3]-sigmatropic rearrangement/ynamide-keteniminium tautomerisation (Scheme 1b). 11 Building on this study, we reasoned that if this substrate class could be prevented from undergoing the posited initial [3,3]-sigmatropic rearrangement step, a change in the chemoselective outcome of the reaction might ensue.…”