Reactions of enamines with dehydroaromatic compounds

Gingrich, Henry L.; Qing-yun, Huang; Morales, A.L.; Jones, Maitland

doi:10.1021/jo00040a016

Cited by 34 publications

(18 citation statements)

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“…[19] However, these are also prone to ene reactions. [20] Enolate additions to arynes have proven to be of exceptional synthetic value. These reactions proceed through the intermediacy of benzocyclobutenols and directly yield products of σ-bond insertion.…”

Section: Introductionmentioning

confidence: 99%

Cycloaddition of Arynes and Cyclic Enol Ethers as a Platform for Access to Stereochemically Defined 1,2‐Disubstituted Benzocyclobutenes

et al. 2014

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Benzocyclobutenes (BCBs) are important entities in a multitude of areas, such as complex organic synthesis, materials and polymer chemistry, and electronics. Whereas reactions between arynes and ketene acetals have been well studied, reactions with cyclic enol ethers are unknown. A cis olefin geometry in cyclic enol ethers makes them well suited for formal [2 + 2] cycloaddition with arynes than for competing ene reactions, making them effective reactants. Reactions of 2,3-dihydrofuran, 2,3-dihydro-3H-pyran, 5-butyl-2,3-dihydrofuran, (S)-2-((benzyloxy)methyl)-2,3-dihydrofuran, and 1,4-dioxene with various arynes were successful. An advantage of the use of cyclic enol ethers is that despite the plausible intermediacy of zwitterionic intermediates, the products are limited to a cis ring junction. This can be exploited for potential access to stereochemically-defined 1,2-disubstituted BCBs. As a demonstration, ether ring cleavage with BBr3 provided trans-functionalized BCBs and displacement with azide then provided cis derivatives. DFT computations have been utilized to understand the structures of three arynes in relation to the cycloadditions and for a predictive evaluation of product ratios in two cases. A comparative evaluation of the HOMO energies of a related series of cyclic olefins has also been performed by DFT computations.

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Section: Introductionmentioning

confidence: 99%

Cycloaddition of Arynes and Cyclic Enol Ethers as a Platform for Access to Stereochemically Defined 1,2‐Disubstituted Benzocyclobutenes

et al. 2014

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“…[13] It was noted that the stability of 1 is dependent upon the counterion used and BF 4 À offers the highest thermal stability of the salt among the anions, such as PF 6 À and Cl À , examined. To test our hypothesis, a benzene suspension of 1 was treated with 1 equivalent of nBuLi at room temperature for 10 minutes to give the expected [4+2] cycloaddition product 3 a in 38 % yield upon isolation (entry 1, Table 1).…”

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confidence: 99%

“…[14] When the non-nucleophilic base lithium diisopropylamide (LDA) was used, 3 a was obtained in 72 % yield (entry 2). Other less-nucleophilic bases gave relatively lower yields (entries [3][4][5]. Increasing the amount of base did not improve the yield (entry 6).…”

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confidence: 99%

1,3‐Dehydro‐o‐Carborane: Generation and Reaction with Arenes

2014

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Like the importance of benzyne, witnessed in modern arene chemistry for decades, 1,2-dehydro-o-carborane (o-carboryne), a three-dimensional relative of benzyne, has been used as a synthon for generating a wide range of cage, carbon-functionalized carboranes over the past 20 years. However, the selective B functionalization of the cage still represents a challenging task. Disclosed herein is the first example of 1,3-dehydro-o-carborane featuring a cage C-B bond having multiple bonding characters, and is successfully generated by treatment of 3-diazonium-o-carborane tetrafluoroborate with non-nucleophilic bases. This presents a new methodology for simultaneous functionalization of both cage carbon and boron vertices.

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“…One results from the interactions between the ipso carbon and the "fatty" cage in 1,4-addition fashion, and the other comes from the steric repulsions between the substituent R and the flanking cage B(3,6)-H hydrogen atoms in 2,5-addition fashion. 14 For toluene and its derivatives 3a,d,e,f as well as trimethylsilylbenzene 3c, the corrected relative reactivities of 1,4-over 2,5-addition lie around 1, which indicates that the differences between the two types of steric interactions are small (Table 1, entries 1 and 3−6). On the other hand, remarkable differences were observed in the reactions of both tert-butylbenzene 3b and p-xylene 3g, as suggested by the corrected ratio of 1,4-over 2,5-adduct (Table 1, entries 2 and 7).…”

Section: ■ Results and Discussionmentioning

confidence: 98%

Reaction of Carboryne with Alkylbenzenes

Wang

Xie

2012

Organometallics

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Carboryne (1,2-dehydro-o-carborane), in situ generated from the precursor 1-iodo-2-lithiocarborane, reacted with alkylbenzenes to give two regioisomers of the [4 + 2] cycloadducts as the major products in moderate to good yields, in which the steric factors play an important role in the regioselectivity. Minor products derived from benzylic C−H insertion reaction, annulation reaction, tandem [4 + 2] cycloaddition/homo Diels−Alder reaction, and tandem ene reaction/[2 + 2] cycloaddition were also isolated and characterized in the reaction of carboryne with toluene. The presence of AgF in the above reaction produced no notable changes in the product distributions and yields.

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Reactions of enamines with dehydroaromatic compounds

Cited by 34 publications

References 0 publications

Cycloaddition of Arynes and Cyclic Enol Ethers as a Platform for Access to Stereochemically Defined 1,2‐Disubstituted Benzocyclobutenes

Cycloaddition of Arynes and Cyclic Enol Ethers as a Platform for Access to Stereochemically Defined 1,2‐Disubstituted Benzocyclobutenes

1,3‐Dehydro‐o‐Carborane: Generation and Reaction with Arenes

Reaction of Carboryne with Alkylbenzenes

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