Hetero-Diels–Alder reaction of aromatic aldehydes catalyzed by titanium tetrachloride: computational and experimental results

Sogani, N. C.; Sinha, Pragya; Bansal, R. K.

doi:10.1016/j.tet.2013.11.077

Cited by 9 publications

(7 citation statements)

References 43 publications

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“…To evaluate the catalytic ability of the trityl ion, 5.0 mol‐% of a series of Lewis and Brønsted acids were screened as catalyst for the oxa‐Diels–Alder reaction. BF 3 · OEt 2 , HBF 4 · OEt 2 , and TiCl 4 9b were found to be potent catalysts, although substantially less efficient than the trityl ion (Table 1, entries 5–7 vs. entry 1). Furthermore, AlCl 3 was completely inactive as a catalyst for this reaction (Table 1, entry 8).…”

Section: Resultsmentioning

confidence: 99%

Carbocation Catalysis: Oxa‐Diels–Alder Reactions of Unactivated Aldehydes and Simple Dienes

El‐Remaily

Naidu

et al. 2015

Eur J Org Chem

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The versatility of the trityl cation (TrBF4) as a highly efficient Lewis acid organocatalyst is demonstrated in the oxa‐Diels–Alder reaction of various unactivated aromatic and aliphatic aldehydes and simple unactivated dienes, such as isoprene and 2,3‐dimethylbutadiene. The transformation proceeds smoothly to give 3,6‐dihydropyrane adducts in high to moderate yields with catalyst loadings down to 1.0 mol‐% under mild reaction conditions. In contrast to most previously reported strategies, this protocol does not require substrate functional group activation, neither by electron‐deficient aldehydes (2‐oxo aldehydes) or electron‐rich dienes (methoxy or amino‐butadiene).

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Section: Resultsmentioning

confidence: 99%

Carbocation Catalysis: Oxa‐Diels–Alder Reactions of Unactivated Aldehydes and Simple Dienes

El‐Remaily

Naidu

et al. 2015

Eur J Org Chem

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“…To further annotate the coordination of the aldehydes to the paramagnetic Fe(III) center, the variable-temperature 19 F NMR spectroscopic study was conducted with p-fluorobenzaldehyde.…”

Section: H Nmr Spectroscopymentioning

confidence: 99%

“…Hence, the reaction commands the use of a very strong Brønsted acid intending to activate the unresponsive heterodienophile to a sufficient extent for compensating the low reactivity of simple dienes. In the early reports, Pd(II) catalysts, Sc(OPf) 3 , TiCl 4 , HOTf, or a mixture of strong Lewis acid AlCl 3 and nitroalkane or SnCl 4 with nitroalkane was subjected to the ODA reactions . In 2012, Matsubara and co-workers reported a big breakthrough of ODA reaction between unactivated dienes with unactivated aldehydes under mild reaction conditions catalyzed by cationic iron(III) porphyrin or iron(IV) corrole complexes .…”

Section: Introductionmentioning

confidence: 99%

“…In the present investigation, a novel, earth-abundant dication diiron(III) porphyrin dimer has been used to catalyze the ODA reaction of unactivated aldehydes and simple dienes under relatively mild conditions with a catalytic loading as low as 1.25 mol % (Scheme 2), which previously had limited opportunities in the presence of the unsaturated bonds (e.g., alkene, alkyne, nitrile, or nitro groups), and with high functional-group tolerance (halide, ether, imide, acetal, or acetoxy groups). Various spectroscopies, like ultraviolet−visible−near-infrared (UV−vis−NIR), 19 F and 1 H nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), electrospray ionization mass spectrometry (ESI-MS), and infrared (IR) integrated with well-synced density functional theory (DFT) results, enabled us to comprehend the reaction mechanism intricately, formerly unrevealed. In addition to this, the dimeric catalyst displays its remarkable efficiency over its monoheme analogue, which in turn dictates the cooperative nature of the dimeric catalyst.…”

Section: Introductionmentioning

confidence: 99%

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Cooperativity in Diiron(III)porphyrin Dication Diradical-Catalyzed Oxa-Diels–Alder Reactions: Spectroscopic and Mechanistic Insights

Sarkar

Samanta

et al. 2022

ACS Catal.

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Here, we delineate a maiden example of a diiron(III) dication diradical porphyrin dimer as a competent catalyst for the oxa-Diels–Alder type reaction of aldehydes with 1,3-dienes, which is a cardinal reaction in the syntheses of natural products. This catalyzed process does not demand the use of electron-deficient aldehydes such as glyoxylic acid derivatives or activated electron-rich 1,3-dienes such as Danishefsky’s, Brassard’s, or Rawal’s diene. The robust catalyst exhibited high functional group tolerance. The computational studies corroborated the detailed spectroscopic investigation, which focused on the pivotal roles played by the metal ion as the Lewis acidic center in combination with counteranions and also enabled us to delve deeper into the reaction mechanism. Previously developed methodologies invariably require dissociation of the iron-axial bond of the catalyst; on the contrary, the axial ligand of the catalyst remains intact during the catalysis reported here. The use of a dication diradical iron(III)porphyrin as the Lewis acid catalyst facilitates activation of the aldehyde via coordination whose formation has also been confirmed experimentally. Moreover, the counteranion has a considerable effect on the reaction pathway; its coordination to the metal inhibits the coordination of the substrate to form the product. The efficacy of employing such a diheme catalyst over a monoheme analogue is manifested in the cooperative effect, which resulted in a lower catalyst loading with excellent yields.

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“…In addition, theoretical studies have been carried out to identify the mechanism involved in the titanium-mediated hetero-Diels-Alder [46,47]. Both studies highlights the formation of a zwitterionic intermediate arising from a stepwise mechanism.…”

Section: Titanium (Ti)mentioning

confidence: 99%

Metal Promoted Diels-Alder Reactions

Gallier¹

2016

COC

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Hetero-Diels–Alder reaction of aromatic aldehydes catalyzed by titanium tetrachloride: computational and experimental results

Cited by 9 publications

References 43 publications

Carbocation Catalysis: Oxa‐Diels–Alder Reactions of Unactivated Aldehydes and Simple Dienes

Carbocation Catalysis: Oxa‐Diels–Alder Reactions of Unactivated Aldehydes and Simple Dienes

Cooperativity in Diiron(III)porphyrin Dication Diradical-Catalyzed Oxa-Diels–Alder Reactions: Spectroscopic and Mechanistic Insights

Metal Promoted Diels-Alder Reactions

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