A Facile Asymmetric Synthesis of 1,2,3-Substituted Indenes

Romines, Karen R.; Lovasz, K. D.; Mizsak, S. A.; Morris, Jeanette K.; Seest, Eric P.; Han, Fusen; Tulinsky, John; Judge, Thomas M.; Gammill, Ronald B.

doi:10.1021/jo9819638

Cited by 29 publications

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References 16 publications

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“…[4] Despite the unquestionable interest of optically active indenes bearing a stereogenic center at C1, as far as we know, only two closely related strategies for the enantioselective synthesis of these compounds from achiral substrates have been published. [5][6][7][8] Both strategies are based on the use of boronic acid derivatives as starting materials and dicationic Pd II complexes as the catalyst. Thus, enantioenriched 1-arylindenes have been obtained in a cascade 1,4addition-aldol condensation process, [5] whereas 1H-indenes bearing a CH 2 COR group at the C1 position are formed from ortho-boronate substituted cinnamic ketones and internal alkynes.…”

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“…[21] To the best of our knowledge, no examples have been reported on the enantioselective cycloisomerization or alkoxycyclization of o-(alkynyl)styrenes. [22] Taking into account the relative success with the use of chiral biphosphines with biphenyl skeletons as ligands in goldcatalyzed enantioselective reactions, we prepared several dinuclear chiral gold(I) catalysts with (R)-binap (L1), (S)-H 8 Initial efforts were focused on selecting an efficient chiral catalyst for the transformation of o-(alkynyl)styrene 1 a into 1-alkenyl-1H-indene 2 a (Table 1). Pleasingly, all chiral gold complexes tested associated with the silver salt AgSbF 6 allowed complete conversions to 2 a in one hour at room temperature ( Table 1, entries 1-8).…”

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Gold(I)‐Catalyzed Enantioselective Synthesis of Functionalized Indenes

et al. 2010

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Molecules containing the 1H-indene scaffold show a wide range of biological activities, [1] and possess great interest as functional materials, [2] as well as precursors of metallocene complexes as for catalytic polymerization processes.[3] So, several methodologies have been developed for their synthesis. [4] Despite the unquestionable interest of optically active indenes bearing the C-1 as stereogenic center, as far as we know, only two closely related strategies for the enantioselective synthesis of these compounds from achiral substrates have been published. [5][6][7][8] Both of them are based on the use of boronic acid derivatives as starting materials and dicationic Pd(II) complexes as catalyst. Thus, enantioenriched 1-arylindenes have been obtained in a cascade 1,4-addition-aldol condensation process, [5] whereas 1H-indenes bearing a CH 2 COR group at the C-1 position are formed from ortho-boronate substituted cinnamic ketones and internal alkynes. [6,7] The scarcity of general methods for the synthesis of optically active indenes (in particular from achiral substrates) aimed us to initiate a project in this field. Our premise was the use of easily available starting materials and, therefore, we fixed our attention on the catalytic cyclization of ortho-(alkynyl)styrenes. In this context, it should be taken into consideration that the skeletal rearrangement of ortho-(alkynyl)styrenes catalyzed by several metallic complexes has been described to afford naphthalene derivatives through a 6-endo cyclization process (Scheme 1, eq. 1).[9-13] However, a careful examination of all these publications showed that reactions with o-(alkynyl)styrenes where the terminal carbon of the alkene was disubstituted were not reported. So, we envisaged that o-(alkynyl)styrenes possessing a highly substituted alkene moiety and an internal acetylene could favour the 5-endo reaction pathway, due to a better stabilization of the exocyclic carbocationic intermediate, to form the desired indene skeleton with a stereogenic center at C-1 (Scheme 1, eq. 2).[14] Herein we report our success on this unprecedented metal-catalyzed 5-endo-dig cyclization of o-(alkynyl)styrenes and the application of this reaction in the synthesis of enantiomerically-enriched indenes. For the initial assays we selected 2´,2´-dimethyl o-(phenylethynyl)styrene 1a as a model substrate (Scheme 2). Due to their excellent ability to activate alkynes, [15] several complexes derived from coinage metals and platinum were tested as catalysts for the desired transformation. However, no reaction was observed with metal complexes such us AgSbF 6 , PtCl 2 , [PtCl 2 (cod)], CuI, AuCl 3 , AuCl or [AuCl(Ph 3 P)]. Encouragingly, the reaction proceeded to completion within 30 min to yield the indenyl derivative 2a in a high isolated yield (88%), when it was performed in dichloromethane at room temperature in the presence of the cationic gold(I) complex generated in situ from 5 mol% of [AuCl(Ph 3 P)] and 5 mol% of AgSbF 6 .[16] Moreover, when this reaction was conducted in the p...

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Gold(I)‐Catalyzed Enantioselective Synthesis of Functionalized Indenes

et al. 2010

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“…3 Thus, a significant effort continues to be given to the development of new indene-based structures and new approaches for their construction. [4][5][6][7] Among the family of indenes, 1-methyleneindenes have attracted much attention recently since they can be easily transferred to functionalized indenes. Although several methods have appeared for the formation of 1-methyleneindene derivatives, 8 development of novel and efficient routes for the generation of functionalized 1-methyleneindenes under mild conditions is still of high interest.…”

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Rapid access to 1-methyleneindenes via palladium-catalyzed tandem reactions of 1-(2,2-dibromovinyl)-2-alkynylbenzenes with arylboronic acids

Yang

2010

Chem. Commun.

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“…An alternative, but seemingly less direct approach, was employed. The aldol condensation of ( S )‐ 18 17 with 19 under the TiCl 4 /sparteine18 conditions afforded a pleasing surprise and not only led to the catenation of the two moieties but also resulted in the simultaneous elimination of the hydroxy group from the intermediate aldol to provide the desired compound 20 directly. Notably, 60 % of the added sparteine was recovered after the aldol reaction by carrying out a simple acid‐base wash and extraction 19…”

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Enantioselective Synthesis of Four Natural Homoisoflavonoids

Zhu

et al. 2015

Eur J Org Chem

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Four naturally occurring sappanin‐type homoisoflavonoids were synthesized in optically active form with the stereogenic centers of predefined absolute configuration constructed by using Evans' asymmetric aldol reaction. Analysis of the synthesized compounds not only confirmed the previously assigned planar structures but also was used to determine the absolute configurations of the natural products. Errors in previously reported NMR signals/solvents are also revealed.

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A Facile Asymmetric Synthesis of 1,2,3-Substituted Indenes

Cited by 29 publications

References 16 publications

Gold(I)‐Catalyzed Enantioselective Synthesis of Functionalized Indenes

Gold(I)‐Catalyzed Enantioselective Synthesis of Functionalized Indenes

Rapid access to 1-methyleneindenes via palladium-catalyzed tandem reactions of 1-(2,2-dibromovinyl)-2-alkynylbenzenes with arylboronic acids

Enantioselective Synthesis of Four Natural Homoisoflavonoids

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