Vinylic cations from solvolysis. 41. Solvolytic rearrangements of 2,2-dianisyl-1-tolylvinyl bromide and (E)- and (Z)-1,2- dianisyl-2-tolylvinyl bromide

Abstract

Solvolytische Umlagerungen der Vinylbromide (I) oder (II) werden diskutiert.

Solvolytic rearrangement studies with (E)- and (Z)-2-anisyl-1,2-ditolyl[2-13C]vinyl bromides

“…The results, as summarized in Table 1, show a remarkably reproducible extent of 37.4-37.5% scrambling for the reaction of (E,Z)-or (E)-6-Br-2-I3C in HOAc-AgOAc, the scrambling being the result of 1,2-anisyl shifts in cation 6. The formation of a 1:l mixture of (E)-and (z)-6-OAc-1 ,2-I3C with the same extent of scrambJing from reaction of either (E,Z)-6-Br-2-13C or (~) -6 -~r -2 -l~~ would indicate the formation of the dissociated, linear 2-anisyl-l,2-ditolylvinyl cation 6 as intermediate in these reactions, a conclusion that is in agreement with those drawn previously in support of dissociated, linear triarylvinyl cations (3)(4)(5).…”

“…For triarylvinyl derivatives with two identical aryl groups, the trans isomer would have a higher melting point. From observations of the chemical shifts in the 'H nmr spectra of cis and trans pairs of triarylvinyl derivatives, it was suggested that for the lower melting cis isomer, the methoxy protons of an anisyl group should appear at higher field and the methyl protons of a tolyl group should appear at lower field than those for the corresponding trans isomer (4,8,9). For (E)-and (Z)-1,2-dianisyl-2-tolylvinyl bromides ((E,Z)-8-Br), a crystallographic study did show that the lower melting isomer with methoxy absorptions at higher fields and a methyl absorption at lower field was indeed the (E) or cis isomer (4).…”

“…'Calculated from eq. [4] or [5], using the mean % scrambling values. "From reaction with CF,COOH-CF,COOAg.…”

“…In addition, cations 2, 3, and 6 should also be able to give a nondegenerate 1,2-phenyl or 1,2-tolyl shift to a more stable 4 5 6 In the case of eq. [2], a nondegenerate rearrangement from a less + + + stable to a more stable vinyl cation, which may occur before and An(Ph)C=CAn An(Tol)C=CAn ( A~I )~C = C A~ after the degenerate rearrangement, as illustrated in eq.…”

Structures of (Z)- and (E)-1,2-diphenyl-2-(4-tolylvinyl) bromide

“…Other bond lengths and bond angles are in agreement with those reported for other triarylvinyl bromides (Wanigasekera et al, 1984;Kaftory, Biali & Rap ° poport, 1985). All aryl rings are also planar in the (Z)-isomer and the molecule adopts a conformation similar to that of the (E)-isomer.…”