Low-temperature-stable sulfonium ion adducts were generated by addition of mono-and disulfides to TiCl 4 -catalyzed quasiliving polyisobutylene (PIB). The adducts were studied in situ via low temperature NMR in 50/50 (v/v) CS 2 /CD 2 Cl 2 using the initiator 2-chloro-2,4,4-trimethylpentane (TMPCl) and C 16 and C 20 tertchloride oligo-isobutylenes as models for the PIB chain end. At temperatures less than or equal to -60 °C, quantitative 1:1 adducts were formed between the (di)sulfides and TMPCl or the oligo-isobutylenes. Adduct formation prevented further homopolymerization of isobutylene, but when a more reactive nucleophile such as an alcohol or amine was added to the reaction, the adducts were destroyed. Both elimination and substitution products were obtained at the PIB chain end. With PIB-monosulfide adducts, elimination was the principle decomposition pathway, and near-quantitative formation of exo-olefin PIB was achieved upon termination by a hindered tertiary amine, such as proton trap, 2,6-di-tert-butylpyridine. For PIB-disulfide adducts, decomposition was observed to occur principally through sulfur-sulfur cleavage, yielding useful thioether end groups, e.g., when terminated with triethylamine, the PIB-bis(2-bromoethyl) disulfide adduct yielded near-quantitative primary bromide-terminated PIB.
Experimental SectionMaterials. Titanium (IV) tetrachloride (99.9%), hexane (95%, anhydrous), 2,6-lutidine (26Lut, 99+%, redistilled), carbon disulfide (99.9%), and dichloromethane-d 2 (99.9% D) were used as received from Sigma-Aldrich. Isobutylene (IB) from BOC and methyl chloride (MeCl) from Alexander Chemical Corp. were passed through columns of CaSO 4 /molecular sieves/CaCl 2 and condensed within a N 2 -atmosphere glovebox immediately prior to use.
A polylithiated β‐ketoester, β‐diketone, or β‐ketoamide was condensed‐cyclized with lithiated methyl 2‐(aminosulfonyl)benzoate, to afford new 3‐substituted 1,2‐benzisothiazole 1,1‐dioxides. Some Grignard or organolithium reagents were also condensed‐cyclized with methyl 2‐(aminosulfonyl)benzoate to give 3‐substituted 1,2‐benzisothiazole 1,1‐dioxides.
Several β‐ketoesters were dilithiated with an excess of lithium diisopropylamide, followed by condensation with methyl 2‐(aminosulfonyl)benzoate to give intermediates that were not isolated but cyclized to 3‐substituted 1,2‐benzisothiazole‐1,1‐dioxides. In most instances involving the ester‐sulfonamide, a single β‐ketoester tautomer is usually formed after recrystallization from ethanol. The same dilithiated β‐ketoesters generally condense less well with 1,2‐benzisothiazol‐3(2H)‐one‐1,1‐dioxide (saccharin) under the same conditions to afford the same products usually in the same or lower yields. The use of N,N,N',N'‐tetramethylethylenediamine during these syntheses has sometimes resulted in improved yields of products.
Several dilithiated C( ),O-oximes were prepared in excess lithium diisopropylamide-tetramethylethylenediamine (LDA/TMEDA) and condensed with methyl 2-(aminosulfonyl)benzoate followed by acid cyclization of intermediates to spiro(benzoisothiazole-isoxazole) dioxides, a new spiro and fused-ring system. Distortionless enhancement by polarization transfer (DEPT) and liquid chromatography mass spectrometry (LCMS) for all products, as well as X-ray single crystal analysis on a representative product, were especially relevant for structure confirmation in this synthesis.
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