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

Abstract

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 ...

The migratory aptitudes of some aryl groops in triarylvinyl cations

“…product to the corresponding 1.2.2-triarylethanol and any unconsumed reactant to triarylethene (9). Separation of the alcohol from the olefin was effected by passage through an alumina column in a similar way as recently described for the separation of 1.2,2-triani~yl[i,2-~~C]ethanol and 1,2,2-trianisy1[1.2-I4C]ethene (13). The triarylethanols so obtained from the reactions with c i~-and trc1ns-QBr-2-~~C and with 5-Br-2-I3C were analyzed by "C nmr in the same way as reported earlier (4.5) to give the results summarized in Table 1. S f~~l i e .~ ~c,ifh ci5-atzd tran~-PBr-2-'~C unil ~t'irh 5-Br-2-I4C The I4C-labeled substrates were prepared in the same way as the analogous "C-labeled bromides.…”

“…derived from the unconsun~ed reactant. was diluted with inactive carrier and subjected to degradation by ozonolysis (13) to give the corresponding diary1 ketone. whose 14C activity indicated no appreciable scrambling of the label in the recovered reactant in all four experiments.…”

Rearrangement studies with 14C. XLIV. Ion-pairs and dissociated ions in the solvolysis of triphenyl[2-14C]vinyl and trianisyl[2-14C]vinyl bromides in 70% acetic acid – 30% water

“…The labeled 1-Br-2-14C and ZBr-2-14C were prepared as previously described (3,5,9). The solvolyses in 70% HOAc, carried out in sealed tubes, have also been described earlier (8 reduction to 1,2,2-triphenylr l ,2-14C]ethanol (4 1 ,2-14C) followed by KMn04 oxidation to diphenyl [14C]ketone (5-14C) to give the extent of scrambling of the label from C-2 to C-1.…”

“…Degenerate rearrangements from 1 ,2-phenyl or 1 ,2-anisyl shifts in triphenylvinyl or trianisylvinyl cationic systems have been investigated under a variety of conditions (3)(4)(5)(6)(7)(8)(9). It is generally agreed that the dissociated "free" trianisylvinyl cation can be formed from trianisylvinyl substrates (6,7,9,10). However, the extent of scrambling observed during solvolyses of triphenyl [2-14C]vinyl triflate (1-OTf-2-14C) in HOAc, HCOOH, or CF,COOH was found to be unaffected by the presence of 1.1 equiv.…”

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

“…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.…”