Diels–Alder reaction of 2-phosphaindolizines catalysed by organoaluminium reagent: theoretical and experimental results

Jangid, Rajendra K.; Gupta, Neelima; Bansal, R. K.; Hopffgarten, Moritz von; Frenking, Gernot

doi:10.1016/j.tetlet.2011.02.007

Cited by 22 publications

(4 citation statements)

References 21 publications

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“…Encouraged by the results described above, we attempted the DA reaction of 3-ethoxycarbonyl-1-methyl-2-phosphaindolizine (17a) with DMB in the presence of ethylaluminum dichloride (EtAlCl 2 ) as a promoter. A clean reaction occurred (Scheme 9) as revealed by the 31 P NMR chemical shift of the product, δ = -5.3, 29 which was in accordance with the 31 P NMR chemical shifts reported for the [2+4] cycloadducts obtained from the DA reactions of P-W(CO) 5 complexes of λ 3 -phosphines. 30 Other 2-phosphaindolizine derivatives reacted in a similar manner.…”

Section: Organo-aluminum Chloride Catalyzed Diels-alder Reactions Of 2-phosphaindolizinessupporting

confidence: 84%

Diels–Alder Reactions with the >C=P– Functionality of Annelated Azaphospholes

Bansal

Kour

2015

Synlett

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The >C=P-functionality in annelated azaphospholes acts as a dienophile and undergoes Diels-Alder reactions with dienes. 1,3-Bis(alkoxycarbonyl)-2-phosphaindolizines react with dienes even in the absence of a catalyst; however, in the presence of an oxidizing agent such as sulfur or selenium, the reaction is much faster. 3-Alkoxycarbonyl-2-phosphaindolizines with an electron-withdrawing group exclusively at position 3 undergo the Diels-Alder reaction only in the presence of a Lewis acid. Density functional theory calculations reveal strong hyperconjugative interactions between the nitrogen lone pair and the >C=P-functionality of the 3-alkoxycarbonyl-2-phosphaindolizine, making it electron-rich. However, in 1,3-bis(alkoxycarbonyl)-2-phosphaindolizines, the ester group at the position 1 acts as a sink for the lone pair of electrons of nitrogen leaving the >C=P-functionality sufficiently electron-deficient to undergo the Diels-Alder reaction.

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Section: Organo-aluminum Chloride Catalyzed Diels-alder Reactions Of 2-phosphaindolizinessupporting

confidence: 84%

Diels–Alder Reactions with the >C=P– Functionality of Annelated Azaphospholes

Bansal

Kour

2015

Synlett

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“…Thus, the phosphinine-η 1 -P-W(CO) 5 complex reacted with 1,3-dienes to afford [2 + 4] cycloadducts. By following the same strategy, we recently reported our theoretical and experimental results of the DA reactions of 2-phosphaindolizine-η 1 -P-AlEtCl 2 complexes [21]. Theoretical calculations at the DFT (B3LYP/6-31+G**) level indicated lowering of the activation barrier by 6 kcal mol –1 for the reaction of σ 2 ,λ 3 - P -coordinated 2-phosphindolizine to methylaluminium dichloride with 1,3-butadiene as compared to that for the corresponding reaction of the uncomplexed 2-phosphaindolizine.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

Jangid¹,

Sogani²,

Gupta³

et al. 2013

Beilstein J. Org. Chem.

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SummaryThe Diels–Alder reaction of the 2-phosphaindolizine-η1-P-aluminium(O-menthoxy) dichloride complex with dimethylbutadiene was investigated experimentally and computationally. The >C=P– functionality of the complex reacts with 2,3-dimethylbutadiene with complete diastereoselectivity to afford [2 + 4] cycloadducts. Calculation of the model substrate, 3-methoxycarbonyl-1-methyl-2-phosphaindolizine-P-aluminium(O-menthoxy) dichloride (7a), at the DFT (B3LYP/6-31+G*) level reveals that the O-menthoxy moiety blocks the Re face of the >C=P– functionality, due to which the activation barrier of the Diels–Alder reaction of 7a with 1,3-butadiene, involving its attack from the Si face, is lower. It is found that in this case, the exo approach of the diene is slightly preferred over the endo approach.

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“…Guided by the above results, we accomplished successfully the DA reaction of 3-(alkoxycarbonyl/acyl)-1-methyl-2-phosphaindolizines ( 38 ) with DMB in the presence of ethylaluminium dichloride as a promoter (i.e., using its 1 equiv.) in dichloromethane at r.t. under nitrogen atmosphere ( Scheme 11 ) [ 38 ]. The occurrence of a clean reaction was revealed by 31 P NMR signal at δ = −16.6 to −5.3 ppm, which is in accordance with the 31 P NMR chemical shifts reported for the [2+4] cycloadducts obtained from the DA reaction of P-W(Co) 5 complexes of λ 3 -phosphinines [ 39 ].…”

Section: Reactions Responsementioning

confidence: 99%

Synergy between Experimental and Theoretical Results of Some Reactions of Annelated 1,3-Azaphospholes

Bansal

Kour

2018

Molecules

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Computational calculations have been used successfully to explain the reactivity of the >C=P- functionality in pyrido-annelated 1,3-azaphospholes. Theoretical investigation at the Density Functional Theory (DFT) level shows that the lone pair of the bridgehead nitrogen atoms is involved in extended conjugation, due to which electron density increases considerably in the five-membered azaphosphole ring. The electron density in the azaphosphole is further enhanced by the presence of an ester group at the 3-position making the >C=P- functionality electron-rich. Thus, 1,3-azaphospholo[5,1-a]pyridine, i.e., 2-phosphaindolizine having ester group at the 3-position only does not undergo Diels-Alder (DA) reaction with an electron rich diene, such as 2,3-dimethyl-1,3-butadiene (DMB). However, an ester group at 1-position acts as electron-sink, due to which transfer of the electron density to the >C=P- moiety is checked and DA reaction occurs across the >C=P- functionality. The coordination of the Lewis acid to the carbonyl group at the 3-position raises the activation barrier, while it is lowered remarkably when it is coordinated to the P atom. Furthermore, the attack of 1,3-butadiene on the Si face of the P-coordinated (o-menthoxy)aluminum dichloride complex is a lower activation energy path. Fukui functions could be used to explain relative reactivities of indolizine and 2-phosphaindolizine towards electrophilic substitution reactions.

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Diels–Alder reaction of 2-phosphaindolizines catalysed by organoaluminium reagent: theoretical and experimental results

Cited by 22 publications

References 21 publications

Diels–Alder Reactions with the >C=P– Functionality of Annelated Azaphospholes

Diels–Alder Reactions with the >C=P– Functionality of Annelated Azaphospholes

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

Synergy between Experimental and Theoretical Results of Some Reactions of Annelated 1,3-Azaphospholes

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Diels–Alder reaction of 2-phosphaindolizines catalysed by organoaluminium reagent: theoretical and experimental results

Cited by 22 publications

References 21 publications

Diels–Alder Reactions with the >C=P– Functionality of Annelated Azaphospholes

Diels–Alder Reactions with the >C=P– Functionality of Annelated Azaphospholes

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η1-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

Synergy between Experimental and Theoretical Results of Some Reactions of Annelated 1,3-Azaphospholes

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Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results