Exploratory and mechanistic aspects of the electron-transfer photochemistry of olefin-N-heteroaromatic cation systems

Yoon, Ung Chan; Quillen, Suzanne L.; Mariano, Patrick S.; Swanson, Rosemarie; Stavinoha, Jerome L.; Bay, Elliott

doi:10.1021/ja00343a022

Cited by 74 publications

(54 citation statements)

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“…2) is never isolated. 'There is no apparent reason for this, since radical ion pair coupling at the 4-position of 6", followed by protonation, should lead to the same type of intermediate as 32. At the present time, no reasonable explanation can be offered for the lack of formation of compound 15.…”

Section: Fig 13mentioning

confidence: 78%

Radical ions in photochemistry. 15. The photosubstitution reaction between dicyanobenzenes and alkyl olefins

Borg¹,

Arnold²,

Cameron³

1984

Can. J. Chem.

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Can. J. Chem. 62, (785 (1984). ' The photosubstitution (electron transfer) reaction between 1,4-dicyanobenzene (1) and 2,3-dimethyl-2-butene (2), which gives I-(4-cyanophenyl)-2,3-dimethyl-2-butene (3) and 3-(4-cyanopheny1)-2,3-dimcthyl-I-butene (4). has been extended to other dicyanobenzene-olefin mixtures. Substitution of a cyano group occurs when both 1 or 1,2-dicyanobenzene (5) are irradiated in acetonitrile solution, in the presence of 2 or cyclohexcne (16). Under comparable conditions, 1.3-dicyanobenzene (6) failed to react. Little or no substitut~on was observed in any case when the olefin was methylpropene (19). ' The results for 1 and 5 are in agreement with empirical free energy calculations (Weller equation) for the electron transfer process which, however, fail to explain the general lack of reactivity of 1,3-dicyanobenzene. Phenanthrene (11) has been shown to photosensitize the photosubstitution reaction between dicyanobenzenes and 2. Under these conditions the olefin reacts with 6 predominantly at the 4-position, resulting in overall substitution of a hydrogen atom. This reaction occurs regiospecifically, resulting in the formation of only one of the two possible isomeric side chains. The mechanistic details of these reactions have been substantiated by means of deuterium labelling studies. The aromatic nitriles also undergo photosubstitution by 2, in acetonitrile-methanol solution, resulting in methanol-incorporated products. Whereas reaction with 1 or 5 results in substitution of a cyano group, 6 was observed to give isomeric dicyanocyclohexenes, resulting from initial reaction at the 4-position, followed by reduction. A detailed mechanism for this secondary photoreduction has been substantiated by deuterium labelling studies. The anomalous behaviour of 1,3-dicyanobenzene has been attributed to a difference in the react~vity of the radical anion. marquages par le deutCrium permettent de confirmer les dttails mkcanistiques dc ces rCactions. Les nitriles aromatiques, en solution dans des milanges d'acktonitrile et de methanol, subissent aussi des photosubstitutions par 2; il y a formation de produits ayant incorporC du mCthanol. Alors que la rCaction des composCs 1 ou 5 conduit a la substitution d'un groupe cyano, on a observC que le compost 6 donne des dicyanocyclohextnes isomkres qui resultent d'une rkaction initiale en position 4, suivie d'une riduction. Des Ctudes impliquant des marquages par du deuterium ont permis de confirmer le mCcanisme dCtaillC de cette photorCduction secondaire. On attribue Ie comportement anormal du dicyano-I ,3 benzkne a la diffkrence de rCactivitC de I'anion radical.[Traduit par le journal]

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Section: Fig 13mentioning

confidence: 78%

Radical ions in photochemistry. 15. The photosubstitution reaction between dicyanobenzenes and alkyl olefins

Borg¹,

Arnold²,

Cameron³

1984

Can. J. Chem.

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“…3-Methyl-2-cyclohexen-1-01 (1) was obtained as a researchgrade chemical from Aldrich. 1-Methyl-2-cyclohexen-l-ol(2) [3], 3-methoxy-l -methyl-1 -cyclohexene (3) [4], 3-methoxy-3-methyl-I-cyclohexene (4) [4], 2-methyl-l,3-~yclohexadiene (5) IS], 1-methyl-1,3-cyclohexadiene (6) [6], and 3-methylenecyclohexene…”

Section: Experimental Section Bimolecular Substitution and Its Extentmentioning

confidence: 99%

“…stainless steel column packed with 5 % FFAP on Chromosorh G-AW-DCMS; the operation was repeated until analytical GLC of the purified samples failed to A further problem tackled in the present investigation is the extent and the mechanism of the gas-phase elimination reaction accompanying acid-induced nucleophilic substitution on methylcyclohexenols 1 and 2. In particular, the study is addressed to the evaluation of the intrinsic structural factors determining the occurrence and the regiochemistry of the acid-induced elimination process (4) in oxonium ions I and 11 in the gas phase, where solvation and ion-pairing effects normally complicating similar processes in solution are excluded. …”

Section: + G " ' [Reah] -+Meoh [Rbe]mentioning

confidence: 99%

“…With 0-protonated 2, however, the concerted SN2' pathway (84-95%) prevails over the classical S J one (6-17%). Concomitant [1,2] (E2) and [1,4] elimination (E 2') pathways involve attack of the selected nucleophiles on the oxonium ions from 1 and 2. Their relative extent (E2'/E2:1.78-1.96 (1); 1.43-1.70 (2)) appears only slightly dependent on the nature of the ionic substrate, the nucleophile (whether MeOH or NMe,), and the leaving group (whether H,O or MeOH).…”

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confidence: 99%

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Regioselectivity in the Gas‐Phase Nucleophilic Attack on O‐Protonated 3‐Methyl‐2‐cyclohexen‐1‐ol and 1‐Methyl‐2‐cyclohexen‐1‐ol

Dezi

Lombardozzi

Renzi

et al. 1996

Chemistry A European J

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Our radiolytic study of the occurrence in the gas phase of concerted SN2' reactions on several open-chain allylic oxonium ions generated in the gas phase from the attack of gaseous GA+ acids (GA' = C , H i ( n = l , 2), iC,H:, and (CH,),F+) on suitable substrates is now continued with cyclic allylic alcohols, such as 3-methyl-2-cyclohexen-1-01 (1) and 1-methyl-2-cyclohexen-1-01 (2), with both MeOH and NMe, as neutral nucleophiles. With MeOH as the nucleophile, the substitution reaction exclusively takes place on 1 as the starting compound, whereas when the substrate is 2 it is accompanied by extensive elimination. With NMe,, only the elimination reaction is observed in the same systems. The analysis of the isomeric distribution of the substitution and elimination products allows definition of the corresponding reaction patterns. As for open-chain oxonium ions, the nucleophilic attack on O-protonated 1 and 2 is preceded by significant intramolecular interconversion. Partial unimolecular dissociation of the same ionic intermediates also takes place. After careful evaluation of the extent of these side processes, it is demonstrated that the 0-protonated 1 undergoes the concerted S,2 process with MeOH almost exclusively (> 99 %). With 0-protonated 2, however, the concerted SN2' pathway (84-95%) prevails over the classical S J one (6-17%). Concomitant [1,2] (E2) and [1,4] elimination (E 2') pathways involve attack of the selected nucleophiles on the oxonium ions from 1 and 2. Their relative extent (E2'/E2:1.78-1.96 (1); 1.43-1.70 (2)) appears only slightly dependent on the nature of the ionic substrate, the nucleophile (whether MeOH or NMe,), and the leaving group (whether H,O or MeOH). The effects of both intrinsic structural factors and experimental conditions in determining the SN2'/SN2 and E2'1 E 2 branchings in the selected oxonium ions is discussed and compared with related gas-phase data.

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“…Later in a study of pyridinium salt electron transfer photochemistry we observed that irradiation of N-allyl-or N-methyl-pyridinium perchlorate 4 in methanol leads to efficient formation of the trans,trans-3,5-dimethoxyaminocyclopentenes 6 (Scheme 2). 5 Further investigation of this process demonstrated that the cyclopentene products arise by stereoselective ring opening of the initially formed bicyclic ammonium cations 5.…”

Section: Introductionmentioning

confidence: 99%

Observations Made in Exploring a Pyridinium Salt Photochemical Approach to the Synthesis of (+)-Lactacystin

2008

Bulletin of the Korean Chemical Society

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The key step in a strategy for the synthesis of (+)-lactacystin involving photocyclization reaction of a cyclopenta-fused pyridinium salt has been probed by using a model substrate. Observations made in this effort led to the discovery of a highly unusual cascade process that leads to stereoselective formation of an interesting tricyclic carbamate. The results of this study are presented and discussed in the context of a (+)-lactacystin synthetic approach.

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Exploratory and mechanistic aspects of the electron-transfer photochemistry of olefin-N-heteroaromatic cation systems

Cited by 74 publications

References 0 publications

Radical ions in photochemistry. 15. The photosubstitution reaction between dicyanobenzenes and alkyl olefins

Radical ions in photochemistry. 15. The photosubstitution reaction between dicyanobenzenes and alkyl olefins

Regioselectivity in the Gas‐Phase Nucleophilic Attack on O‐Protonated 3‐Methyl‐2‐cyclohexen‐1‐ol and 1‐Methyl‐2‐cyclohexen‐1‐ol

Observations Made in Exploring a Pyridinium Salt Photochemical Approach to the Synthesis of (+)-Lactacystin

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