Vinylic cations form solvolysis. I. Trianisylvinyl halide system

Abstract

phonium salts which can undergo further decomposition to tetracovalent phosphorus compounds. Experimental SectionMaterials. The starting phosphines were prepared by standard techniques or purchased when possible. Their 1H and 31P nmr spectra agreed with literature values.Reactions. Equimolar quantities (ca. 5 X mol of the phosphine and diethyl peroxide) were allowed to react in methylene chloride. Usually the reactants were cooled to at least 0" before mixing. The reactions were monitored by 1H and 31P nmr spectroscopy. In those studies in which other solvents were used the methylene chloride was evaporated at room temperature in cucuo and the residue was dissolved in the appropriate solvent. Benzoic acid was added to each reaction mixture and the formation of ethyl benzoate was demonstrated by glpc.formed by exchange. Once again the compound 19 is quite unstable and it decomposes readily to tetracovalent phosphorus compounds.The relative instability of the compounds with amino nitrogen bonded to phosphorus is not unexpected. Amino nitrogen can stabilize a positive charge on phosphorus and therefore enhance dissociation to phos-Abstract: Solvolysis of trianisylvinyl chloride (1-CI) and bromide (1-Br) and of l-anisyl-2,2-diphenylvinyl bromide (7) in 80% ethanol follows a first-order course in the substrate, is independent of the concentration of added sodium hydroxide, and is only slightly dependent on that of added p-toluenethiolate ion. The solvolysis of 1-Br is 1.75 times faster than that of a-bromo-p-methoxystyrene, excluding the addition-elimination mechanism. The similar rates for 1-Br and 7 point to the absence of P-aryl participation. The Grunwald-Winstein nz values of 0.34-0.53 and the kl-B,/kl.CI value of 58 at 120" are discussed in terms of intermediate vinylic cations in the solvolysis. The reactivity difference between a-bromostyrene and a-phenylethyl bromide is entirely due to activation energy difference. Vinylic and saturated cations are compared.inylic cations were studied very little until recent V years. Lately, they were suggested as intermediates in electrophilic additions to allenes and acetylenes (eq l),* in the deamination of vinylamine~,~ or in the reaction of 2-oxazolidones in basic solution4 or vinyltriazenes in acidic solution5 (eq 2). Ions with contributing vinylic cation structures were observed by nmr,6 and solvolysis products of acetylenic sulfonates ( I ) Presented in part at

A Search for Unambiguous Vinylic SRN1 Reactions

“…Substrate An 2 CϭCBr 2 (20), with a redox potential (E p ϭ Ϫ2.17 V) similar to 18, in fact gave different behaviour on treatment with the reference nucleophile (Scheme 7). A halophilic route, [1,12] followed by FBW rearrangement, [7] may explain the formation of AnCϵCAn (21), whereas an ETinduced dehalogenation followed by hydrogen abstraction (18) Ϫ2.14 An 2 CϭCHAn Ϫ2.46 An 2 CϭCBr 2 (20) Ϫ2.17 An 2 CϭCHBr (22) Ϫ2.48 An 2 CϭCCl 2 (23) Ϫ2.32 An 2 CϭCH 2 Ϫ2.7 Ph 2 CϭCBr 2 (25) Ϫ1.51 Ph 2 CϭCHBr (15) Ϫ2.24 Ph(Me)CϭCHBr (10) Ϫ2.3 [a] Values in THF at 0.5 V/s vs. SCE. The concentration of the substrate was 2 m, while that of the supporting electrolyte, Bu 4 N ϩ BF 4 Ϫ , was 0.37 .…”

“…The following precursors were prepared according to the literature: triphenylvinyl bromide (3), [2b,22] tris(panisyl)vinyl bromide (18), [23] 1,1-bis(p-anisyl)-2,2-dibromoethene (20), [24] 1,1-bis(p-anisyl)-2,2-dichloroethene (23), [25] 1,1-dibromo-2,2-diphenylethene (25). [26] (E,Z)-1-Bromo-2-phenylpropene (10): Bromination [2b,27] of commercial (Aldrich) α-methylstyrene (2.05 mL, 15.8 mmol), dissolved in CCl 4 (10 mL), with a solution of Br 2 (1 mL, 19.5 mmol) in 20 mL of CCl 4 for 18 h, followed by dehydrobromination [2b] of the dibromo derivative with KOH powder (2.68 g, 40.9 mmol) and 18-crown-6 (35 mg, 0.13 mmol) in boiling hexane (40 mL) for 36 h, gave a brown liquid, which was distilled (bp 104Ϫ108°C at 28 Torr) to give 0.6 g (19%) of a 92:8 (E)/(Z) mixture of pure 10 as an oil: 1 H NMR: δ ϭ 7.4Ϫ7.2 (m, 5 H, Ph), 6 General Procedure for Irradiation Reactions: Under a stream of argon, the substrate (0.2 mmol) was added to a solution of the parent acid of the anion (0.7 mmol) and sublimed tBuOK (0.8 mmol) in 5 mL of Me 2 SO.…”

Solvolysis of 1‐p‐Methoxyphenyl‐2‐Methylpropen‐1‐Yl Trifluoroacetate and 3,5‐Dinitrobenzoate

“…A rough calculation of k , for the reaction of 2,6-lutidine, assuming route c via ion pairs, and using the pKa of 2,6-lutidine in water and k 2 with sodium tritluoroethoxide, gave a k, value which was five-fold lower than the observed value. This result and the (3) difference in activation parameters between 2,6-lutidine and Et 3 N suggest that route b applies for the weak amines. Apparently, the higher concentration of the weak base more than compensates for its lower nucleophilicity in its competition with the low concentration of the better (tritluoroethoxide) nucleophile.…”

“…The solvent isotope effect and the products from I-OONB in AcOH are consistent with an SN 1 mechanism, but since the kCl/kOONB ratio is lower than that in saturated systems, an AAC2 mechanism cannot be unequivocally excluded. The effect of the leaving group in the vinylic SN I reaction is discussed.Many mechanistic routes are available for nucleophilic vinylic substitution [I), and we previously showed that the vinylic SN1 mechanism [2] operates for many a-arylvinyl substrates [3]. Gal had shown [4-6] that competition of this route with electrophilic addition-elimination (Ad E -E) [7] and with nucleophilic additionelimination (Ad N -E) [I] is important for several systems, and competition with the E2 mechanism was also observed [8].With a-activated substituted vinyl sulphonate esters such as trifluoromethanesulphonates (triflates) [9], 2, 4,6-trinitrobenzenesulphonates [10], and tosylates [II), the SNI reaction usually predominates.…”

Rearrangement studies with 14C. XLI. Degenerate rearrangements in vinyl cations from triphenylvinyl-2-14C-phenyltriazene and from trianisylvinyl-2-14C-phenyltriazene

“…Degenerate 1,2-aryl shifts in triarylvinyl cationic systems labeled with 14C or 13C have been investigated in this laboratory (2)(3)(4)(5). It is generally agreed that a-anisyl substituted vinyl systems would give rise to open, classical vinyl cations, and degenerate 1,2-anisyl shifts took place in the classical trianisylvinyl cation (4)(5)(6)(7)(8). However, ion-pairs might be involved in the degenerate 1,2-phenyl shifts observed in solvolyses of triphenylvinyl-2-14C triflate (2).…”