Diastereo- and regioselective Diels–Alder reactions of 2-phosphaindolizines

Bansal, R. K.; Gupta, Neelima; Kumawat, Surendra K.; Dixit, Govind

doi:10.1016/j.tet.2008.04.080

Cited by 22 publications

(7 citation statements)

References 47 publications

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“…In this context, we found that 1,3-bis(alkoxycarbonyl)-2-phosphaindolizines ( 1a , Z = CO 2 R 1 ) prepared through 1,5-electrocyclization of in situ generated bis(pyridinium ylidyl)phosphenium chlorides [17] lead to successful DA reaction [18–19], but 3-alkoxycarbonyl-2-phosphaindolizines having an electron-withdrawing group (EWG) only at the 3-position ( 1b , Z = Me) failed to undergo DA reaction even on heating under reflux in toluene alone or in the presence of sulfur [18] (Scheme 1). …”

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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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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“…© Georg Thieme Verlag Stuttgart • New York -Synlett 2015,26,[294][295][296][297][298][299][300][301][302][303] …”

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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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“…However, to our great surprise, the compounds 3-ethoxycarbonyl-1-methyl-1,3-azaphospholo[5,1- a ]pyridine 10a ( 10 , Z=Me, R 1 =R 2 =R 3 =H) obtained through [4+1] cyclocondensation and 1,3-bis(ethoxylcarbonyl)-1,3-azaphospholo[5,1- a ]pyridine 10b ( 10 , Z=CO 2 Et, R 1 =R 2 =R 3 =H) showed remarkable difference in their reactivity with 2,3-dimethylbuta-1,3-diene (DMB). It was found that 3-(ethoxycarbonyl)-1-methyl-1,3-azaphospholo[5,1- a ]pyridine ( 10a ) did not undergo DA reaction with DMB, even upon boiling in toluene in the presence of sulfur (used to oxidize phosphorus atom of the initially formed cycloadduct to push the reaction in the forward direction, see later) [ 31 ]. But, 1,3-bis(ethoxylcarbonyl)-1,3-azaphospholo[5,1- a ]pyridine ( 10b ) underwent DA reaction with DMB at room temperature (r.t.).…”

Section: Reactions Responsementioning

confidence: 99%

“…However, the reaction at room temperature (ca 25 °C) was very slow and could be completed (δ 31 P NMR = 14.1 ppm) after heating at reflux temperature in chloroform for four days. On carrying out the reaction in the presence of sulfur or methyl iodide, it was complete at r.t. in 4 days [ 31 ]. Thus, the DA reactions of 1,3-bis(ethoxycarbonyl)-1,3-azaphospholo[5,1- a ]pyridines and also of an isoquinoline analogue with DMB and isoprene could be accomplished successfully ( Scheme 5 ) [ 31 , 32 ].…”

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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Diastereo- and regioselective Diels–Alder reactions of 2-phosphaindolizines

Cited by 22 publications

References 47 publications

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

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

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

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

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Diastereo- and regioselective Diels–Alder reactions of 2-phosphaindolizines

Cited by 22 publications

References 47 publications

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

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

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

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

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