Gold Catalysed 1,4-Enyne Acetate Strategy for the Synthesis of 1H-Indenes and Partially Hydrogenated Methanonaphtho[1,2-c]furan-1,3(4H)-diones

Abstract

A synthetic method to prepare 1H-indenes and partially hydrogenated methanonaphtho[1,2-c]furan-1,3(4H)-diones from gold(i)-catalysed 1,4-enyne acetate cycloisomerisation and oxidation or Diels–Alder reaction with maleic anhydride is described. The proposed mechanism involves Rautenstrauch rearrangement of the 1,4-enyne motif to give an insitu formed 1,3-cyclopentadiene intermediate. This is followed by 6-endo-dig cyclisation of the cyclic adduct and oxidation to give the aromatic carbocycle or Diels–Alder reaction with maleic anhydride to afford the bridged furan product.

Recent Advances in the Gold-Catalyzed Reactions of Propargyl Esters

“…31 The initial step of the deacetylative double cycloisomerization reaction was shown to proceed with the Au-5-catalyzed construction of the Rautenstrauch intermediate In contrast, the Lewis and Brønsted acid cooperative catalytic system was found to be inoperative on examining the analogous gold(I)-mediated reactions of the substrate where n = 1 (Scheme 13, paths b and c). 32 In this work, the Brønsted acid-catalyzed stepwise [3 + 2] cycloaddition of the 1,4-cyclopentadienyl intermediate 71 generated from Au-6-catalyzed Rautenstrauch rearrangement of 1,6-diynyl vinyl acetate 66 was not observed. Instead, the isolation of the 1Hindane adduct 74 suggested a pathway involving preferential activation of the Rautenstrauch adduct by the gold(I) salt.…”

“…Despite the discovery of these two modes of reactivity being reported more than 30 years ago, it was only at the turn of this century that further exploration of the field received significant attention. − ,− ,− In the realm of gold catalysis, Ohe, Uemura, and colleagues described the first example of the Au­(III)-mediated [2,3]- and [3,3]-sigmatropic rearrangement of propargyl esters as part of a study exploring the ruthenium­(II)-catalyzed reactivity of the substrate class (Scheme ). Under the reported reaction conditions, propargyl acetate 7 was shown to react with styrene 8 to afford cyclopropane 9 as well as allenyl acetate 10 in 63 and 26% yield, respectively.…”

“…Another reactivity mode that has been at the forefront of our minds was the development of cascade pathways initiated by the gold­(I)-catalyzed [2,3]-sigmatropic rearrangement/metallo-Nazarov cyclization of 1,4-enyne esters. ,− Often referred to as the Rautenstrauch rearrangement, our reaction design was guided by early works showing the gold­(I)-catalyzed cycloisomerization as an efficient strategy for the construction of a variety of cyclopentenyl derivatives. − , In the first of these studies, the Rautenstrauch rearrangement/[4 + 2] cycloaddition of 1,4,9-dienyne esters 56 under the Au-6 -catalyzed reaction conditions described in Scheme was found to give the 3a,6-methanoisoindoles 57 in 40–99% yield . The reaction mechanism was reported to proceed by way of an initial gold­(I)-mediated 1,2-acyloxy migration of the substrate to afford the organogold species 59 via the 1,3-dioxol-1-ium adduct 58 , which can undergo either a concerted or stepwise deaurative metallo-Nazarov cyclization.…”

“…Homogeneous catalysis is undoubtedly one of the cornerstones of modern chemical synthesis, and its continuous development has been key to efforts focused on the realization of strategies that enable the efficient and concise assembly of compounds of current biological and materials interest. − Within this broad field of research, one of the main drivers of this progress is transition-metal catalysis, which has provided numerous elegant synthetic methods for complex, exotic molecular structures, such as those seamlessly produced by nature, to be built in an operationally simple and selective manner and with high functional group tolerance. Among the breadth of transition-metal catalysts now available, those based on gold­(I) and gold­(III) stand out due to their ability to exhibit potent σ- and π-Lewis acidity without the problems typically associated with such properties. − ,− The group 11 metal also has a high tolerance to air and moisture and various acid-sensitive functional groups that allows for generally mild reaction conditions to be developed. Added to this is the continuous revealing of new reactivities not seen in other d-block elements due to relativistic effects, which reaches a maximum with gold. , Reflective of this has been the impact of gold catalysis on the reaction chemistry of propargyl esters that has made the compound class an invaluable building block in synthetic method development focused on the rapid increase of molecular complexity in an efficient and selective manner. − Key to this has been the ease with which the gold-carbene species or allenyl ester generated in situ from the 1,2- and 1,3-acyloxy migration of the substrate can be readily telescoped into subsequent cascade bond formation reactions and the assembly of various synthetic targets.…”

“…Added to this is the continuous revealing of new reactivities not seen in other d-block elements due to relativistic effects, which reaches a maximum with gold. , Reflective of this has been the impact of gold catalysis on the reaction chemistry of propargyl esters that has made the compound class an invaluable building block in synthetic method development focused on the rapid increase of molecular complexity in an efficient and selective manner. − Key to this has been the ease with which the gold-carbene species or allenyl ester generated in situ from the 1,2- and 1,3-acyloxy migration of the substrate can be readily telescoped into subsequent cascade bond formation reactions and the assembly of various synthetic targets. In the present Account, we showcase our contributions to this field of reaction discovery directed at revealing new modes of reactivity initiated by a [2,3]- or [3,3]-sigmatropic rearrangement. − ,− It provides an overview of novel synthetic routes to accessing a wide variety of cyclic compounds of potential biological and functional materials value in a single operation driven by homogeneous gold catalysis.…”