The Generation of Vinyl Cations from Vinyltriazenes

Can. J. Chem. 57,1384 (1979. Acetolyses of trianisyl[2-14C]viny1 bromide (1-Br-2-14C) were carried out in the presence of various amounts of added NaOAc or NaOAc and LiBr. Scramblings of the isotopic label from C-2 to C-1 arising from 1,2-anisyl shifts in the trianisylvinyl cation were observed in both the reaction product and the recovered, unconsumed reactant. The results indicate that the relative contribution of the 1,2-shift process is decreased with an increase in the amount of NaOAc or LiBr, in support of a mechanism involving formation of the dissociated trianisylvinyl cation which will competitively undergo 1,Zanisyl shift to give scrambling, be captured by Br-ion and return to scrambled starting material, and be captured by OAc-ion to give scrambled product. The results are also compared with previous data from solvolyses of triphenyl[2-14C]vinyl bromide and the differences are discussed.CHOI CHUCK LEE, URSULA WEBER et CRAIG A. OBAFEMI. Can. J. Chem. 57,1384Chem. 57, (1979. On a effectue l'ac6tolyse du bromure de trianisyl[2-14C]vinyle (1-Br-2-14C) en presence de quantites diverses de NaOAc ou de NaOAc et de LiBr. On a observe des echanges des isotopes marqueurs du C-2 vers C-1 provenant de transpositions-1,2 des anisyles dans le cation trianisylvinyle tant dans le produit de la reaction que dans le reactif r6cup6rk qui n'avait pas rkagit. Les rksultats indiquent que la contribution relative aux transpositions-1,2 diminue avec une augmentation de la quantite de NaOAc ou de LiBr; ceci est en accord avec un mecanisme impliquant la formation du cation trianisylvinyle dissocit qui subira des reactions cornpetitives soit de transpositions-1,2 donnant lieu a des echanges des isotopes soit des reactions oiI l'ion est piege par du Br-et donne lieu a une reaction de retour redonnant le produit de depart oiI il s'est produit des echanges ou des reactions ou Pion est piege par des ions OAc-qui fournissent des produits oiI il s'est effectue un khange. On compare aussi ces rksultats ceux obtenus anttrieurement lors de la solvolyse du bromure de triph&nyl[2-14C]vinyle et on discute des differences.[Traduit par le journal]The degenerate rearrangement arising from a 1,2-anisyl shift across the double bond in the trianisylvinyl (tris(p-methoxypheny1)vinyl)) cation was first reported from this laboratory in 1975 (1). For example, in the reaction of triani~~l[2-~~C]vinyl bromide (1-Br-2-13c) with HOAc-AgOAc, 13C nmr analysis of the product showed about 20% scrambling of the label from C-2 to C-1 (1). Similarly, using D-labeling and l H nmr analysis, Rappoport and co-workers (2) found that the NaOAc buffered acetolysis of 1,2-dianisyl-2-p-(2H3)methoxyphenylvinyl bromide (1-Br-methoxy-d,) gave 35 f 2% rearrangement1 arising from 1,2-anisyl shifts. It was also noted that when the NaOAc buffered acetolysis was carried out in the presence of an excess of Bu4NBr, 4 f 1.5% rearrangement was observed in the recovered reactant (2). Earlier, Rappoport and Gal (3) had reported that the unbuffered acetolysis of 1-Br gave irregular ...

mentioning

confidence: 91%

Rearrangement studies with ¹⁴C. XLIII. The acetolysis of trianisyl[2-¹⁴C]vinyl bromide

Lee¹,

Weber²,

Obafemi³

1979

“…The acid catalyzed decomposition of triazenes presumably proceeds via the diazonium ion which gives rise to the dissociated triarylvinyl cation (6,9). The isotopic scramblings observed in the present system would arise from 1,Zphenyl shifts in the 1,2-dianisyl-2-phenylvinyl cation as depicted in that if one were to consider a bridged ion as a model of the transition state foi the 1 ,2-aryl shift, in going from a linear triarylvinyl cation such as 5 to a bridged transition state such as 6, the higher stability of an a-anisyl substituted vinyl cation would lead to a higher activation energy and hence a lower extent of scrambling.…”

Section: Cmentioning

confidence: 99%

“…mechanism as shown in Scheme I since, in the presence of the more nucleophilic OAc-ion, the scrambling process would compete less effectively with product formation (8)(9)(10). From the actually observed decrease in scrambling, calculations can be made to give the selectivity of the cation in its product forming capture reactions with OAc-and with HOAc, koAclkHOAc.…”

Section: Cmentioning

confidence: 99%

Rearrangement studies with ¹⁴C. XLV. The decomposition of cis- and trans-1,2-dianisyl-2-phenyl[2-¹⁴C]vinylphenyltriazenes in acetic acid

Lee¹,

Obafemi²

1981

Can. J. Chem. 59, 1636 (1981). The decomposition of cis-or trans-l,2-dianisyl-2-phenyl[2-'4C]vinylphenyltriazene (cis-or trans-1-NNNHPh-2-I4C) in HOAc gave a 1: 1 mixture of cis and trans products which showed about 3% scrambling of the label from C-2 to C-1 due to 1,2-phenyl shifts in the 1,2-dianisyl-2-phenylvinyl cation. The presence of the more nucleophilic acetate ion from the addition of different amounts of NaOAc was found to decrease or even completely suppress the extent of isotopic scrambling. Comparisons with earlier data such as those obtained from the decomposition of triani~y1[2-~~C]vinylphenyltriazene (2-NNNHPh-2-I4C) led to a calculated k,,,,/kNPh) of about 25 for the relative anisyl to phenyl migration ratio. A kOAc/kHOAC ratio of about 1.5 x lo3 for the product forming capture reactions in the 1,2-dianisyl-2-phenylvinyl cation from the decomposition of 1-NNNHPh-2-I4C was also obtained.CHOI CHUCK LEE et CRAIG A. OBAFEMI. Can. J. Chem. 59, 1636 (1981). La decomposition des dianisyl-1,2 pher1yl-2['~C-2] vinylphenyltriaz2nes cis ou trans (NNNHPh-1 I4C-2 cis ou trans) dans du AcOH donne un melange I: 1 de produits cis et trans dont le marquage est echangk d'environ 3% entre C-2 et C-1 par suite des deplacements 1,2 du ~h e n~l e du cation dianisyl-1,2 phenyl-2 vinyle. On a trouve que la presence d'un ion acetate plus nuclCophile, provenant de I'addition de differentes quantites de AcONa, diminue ou mime supprime completement le degre d'echange isotopique. Une comparaison avec des donnees anterieures, comme celles obtenues a partir de la decomposition du triani~yl[~~C-2]vinyIphenyltriaztne (NNNHPh-2 14C-2), a conduit a une valeur calculee de k,o,)/k,ph, d'environ 25 pour le rapport de migration de I'anisyle vers le phenyle. On a egalement obtenu un rapport kAcO/kAeOH d'environ 1,5 x lo3 pour le produit engendrant les reactions de capture dans le cation dianisyl-1,2 phenyl-2 vinyle partir de la decomposition du NNNHPh-1 14C-2.[Traduit par le journal]The isomeric cis-and trans-1,2-dianisyl-2-solvolysis in HOAc-NaOAc of a 5: 1 mixture of phenylvinyl bromides and chlorides (cis-and cis-and trans-1-anisyl-2-p-[2H,]methoxyphenyltrans-1-Br and 1-C1) were prepared and their 2-phenylvinyl bromides (cis-and trans-l-Br-2-stereochemistry determined in 1969 by Rappoport methoxy-d,), but some scrambling was observed and Apeloig (1). Solvolytic studies in various sol-in the solvolysis of this D-labeled substrate in vents, with or without added nucleophiles, gave a 1: 1 aqueous ethanol or in 2,2,2-trifluoroethanol. In the mixture of the cis and trans products and it was present work, a study was made on the possible concluded that S,l reactions took place via the degenerate rearrangement from 1,2-phenyl shifts dissociated 1,2-dianisyl-2-phenylvinyl cation. Fur-in the 1,2-dianisyl-2-phenylvinyl cation generated ther work with cis-and trans-1-Br, cis-1-C1, and from the decomposition in HOAc of 1,2-dianisylthe methanesulfonates cis-and trans-1-OMS, in-2-phenyl[2-14C]vinylphenyltriazene (1-NNNHPhcluding kinetic studies ...

“…Rearrangements arising from 1,2-aryl shifts across the double bond in the triarylvinyl cation were also observed by these workers. For example, the decomposition in HOAc of l-phenyl-2,2-di-p-tolylvinylphenyltriazene gave 80% of the unrearranged 1-phenyl-2,Zdi-p-tolylvinyl acetate and 20% of the rearranged 2-phenyl-l,2-di-p-tolylvinyl acetate and this rearrangement was completely suppressed by the presence of 10 molar equivalents of added KOAc (1). These findings were interpreted as being consistent with the formation of the free 1-phenyl-2,2-di-p-tolylvinyl cation which could undergo 1,Ztolyl shift to give the more stable 2-phenyl-1 ,2-di-p-tolylvinyl cation.…”

mentioning

confidence: 99%

Rearrangement studies with ¹⁴C. XLVII. The decomposition of chain labeled or ring labeled trianisylvinylphenyltriazene

Lee¹,

Obafemi²

1982

CHOI CHUCK LEE and CRAIG A. OBAFEMI. Can. J. Chem. 60,2410Chem. 60, (1982. Simultaneous reactions were carried out on the decomposition of the chain labeled triani~yl[2-~~C]vinylphenyltriazene (1-NNNHPh-2-I4C) and the ring labeled 1,2-diani~yl-2-p- [~~C]methoxyphenylvinylphenyltriazene (I-NNNHPh-2-metho~y-'~C) in HOAc, HOAc-NaOAc, or CF3CH20H-HC10,. In HOAc, the presence of increasing amounts of NaOAc resulted in decreasing extents of isotopic scrambling arisingfrom I ,2-anisyl shifts in the trianisylvinyl cation, in agreement with previous observations. For decompositions in the less nucleophilic TFE, complete equilibration was observed, giving rise to 50.0% and 33.3% scramblings, respectively, for the chain and ring labels. When the data were expressed as % rearrangement, with the assumption that 100% rearrangement would correspond to 50.0% or 33.3% scrambling, respectively, for the chain or ring label, for each experiment under a given set of conditions, the % rearrangement was found to be equal in the chain and in the ring label. These results are discussed in conjunction with earlier data from the acetolysis of doubly labeled 1,2-dianisyl-2-p-[1T]methoxyphenyl[2-"C]vinyl bromide (1-Br-2-13C-2-methoxy-14C) which gave, depending on experimental conditions, either equal or unequal values for the % rearrangement in the chain and in the ring Label.CHOI CHUCK LEE et CRAIG A. OBAFEMI. Can. J . Chem. 60,2410Chem. 60, (1982. On a effectue des reactions de decompositions simultanees dans le AcOH, le AcOH-AcONa ou le CF3CH,0H-HCIO, d u trianisyl 12-I4C] vinylphenyltriazkne (1-NNNHPh-2-I4C) marque dans la chaine et du dianisyl-1,2 p-[I4C] methoxyphenyl-2 vinylphtnyltriazkne (I-NNNHPh-2-methoxy-'jC) marque sur le cycle. Dans le AcOH, la presence de quantites croissantes d e AcONa provoque une diminution du taux de melange isotopique provenant de glissements 1,2 des anisyles du cation trianisylvinyle; ceci est en accord avec des observations anterieures. Dans le cas des d6compositions dans le TFE qui est moins nuclCophile, on a observe une equilibration compltte donnant lieu B des taux de melanges respectivs de 50% et de 33% pour les composes avec une chaine ou un cycle marque. Quand on exprime les donnees en %de transposition, en se basant sur le fait qu'une transposition a 100% correspond A un melange de 50.0% ou de 33,3% suivant que le marqueur est sur la chaine ou sur le cycle, o n trouve pour chaque experience conduite dans un ensemble de conditions donnees que le % de transposition est le mkme que le marqueur soit dans la chaine ou dans le cycle. On discute des ces resultats en fonction des donnees anterieures provenant de I'acCtolyse du bromure d e dianisyl-1,2 p[I4C] methoxyphenyl-2 [2-I3C] vinyle doublement marque qui donne, suivant les conditions experimentales, soit des valeurs Cgales ou inegales du % de transposition suivant que le marqueur est dans la chaine ou dans le cycle.[Traduit par le journal]The acid catalyzed decomposition of triarylvinylphenyltriazene as a method of generating the triarylvinyl cat...