R-Butyl group

Analogous products are obtained from thermolyses of chlorodiazirines bearing ethyl, propyl, isopropyl or r-butyl groups. 

The compound was reasonably stable, reverting to the aromatic starting material only on heating. Part of the stability of this particular Dewar beii2ene derivative can be attributed to steric factors. The r-butyl groups are farther apart in the Dewar benzene stracture than in the aromatic structure. The unsubstituted Dewar benzene was successfully prepared in 1963. 

The r-butyl group is introduced as a t-butylamine and is cleaved with strong acid (70-97% yield). ... 

Mohanty et al. were the first to introduce pendent r-butyl groups in die polymer backbones. The resulting material was quite soluble in aprotic dipolar solvents.83 The PEEK precursors were prepared under a mild reaction condition at 170°C. The polymer precursor can be converted to PEEK in die presence of Lewis acid catalyst A1C13 via a retro Friedel-Crafts alkylation. Approximately 50% of die rerr-butyl substitutes were removed due to die insolubility of the product in die solvent used. Later, Risse et al. showed diat complete cleavage of f< rf-butyl substitutes could be achieved using a strong Lewis acid CF3SO3H as both die catalyst and the reaction medium (Scheme 6.15).84... 

Benzo-l,2,3,4-tetrazine 1-lV-oxides 13 can be obtained by intramolecular cyclisation of 2-(r-butylazoxy)phenyldiazonium tetrafluoroborates 11 which leads to 2-(r-butyl)benzo-1,2,3,4-tetrazinium 4-A/ oxides 12 via N to N migration of the r-butyl group followed by... 

The structure of this silaamidide salt consists of well-separated, noninteracting lithium cations [Li(12-crown-4)THF]e and N,N -bis(2,4,6-tri-/-bu-tylphenyl)-f-butylsilaamidide anions. In the anion, the silicon is tricoordi-nated to a carbon atom of the r-butyl group and to two nitrogen atoms. 

Substitution of the 4-nitro group in 3,4-dinitrofuroxan 1176 by ammonia occurs readily, even at low temperature. Subsequent treatment of the obtained amine, product 1177, with r-butylamine results in formation of 4-amino-2-(/-butyl)-5-nitro-l,2,3-triazole 1-oxide 1178. However, there must be some additional side products in the reaction mixture, as the isolated yield of compound 1178 is only 17%. Upon treatment with trifluoroperacetic acid, the r-butyl group is removed. The obtained triazole system can exist in two tautomeric forms, 1179 and 1180 however, the 1-oxide form 1179 is strongly favored (Scheme 195) <2003CHE608>. 

The course of the enantioselectivity is interpreted in terms of a side-on approach by the substrate to the active oxomanganese(Y) intermediate (Fig. 4-6). The results of the epoxidation are shown in Scheme 4-40.84,91 To achieve higher enantioselectivities, sterically demanding r-butyl groups substituted at the C3 and C3 positions in the salen complex have proved to be essential. 

The benzyl anion of l-benzyloxy-2,2,4,4-tetramethylpentan-3-ones undergoes intramolecular nucleophilic addition to the carbonyl group without competing Wittig rearrangement or decomposition the stereoselectivity observed is consistent with avoidance of interaction between aryl and r-butyl groups. 

ANRORC process, i.e., adduct formation at C-5, is not prevented by these groups. This is a remarkable effect, certainly when taking into consideration the bulkiness of the r-butyl group, which could be expected to diminish the participation of the ANRORC process. It demonstrates that the... 

Factors which affect the oxepin-benzene oxide equilibrium positions are similarly expected to influence the thiepin-benzene episulfide distribution at equilibrium. Since however the thianorcaradiene tautomer has not to date been detected, the main evidence for this form is based upon the thermal instability and reactions of the thiepin system. Thus it is assumed that where the thianorcaradiene isomer is present, a spontaneous thermal decomposition involving extrusion of a sulfur atom will occur. Substitution at the 2,7-positions in the oxepin-arene oxide system leads to a preference for the seven-membered ring form and this effect was further enhanced by bulky substituents (e.g. Bu ). A similar effect was observed in thiepins and thus the remarkable thermal stability of (49) (2,7-r-butyl groups) and (51) (2,7-hydroxyisopropyl groups) contrasts with the behavior of thiepin (55)(2,7-isopropyl groups), which was thermally unstable even at -70 °C (78CL723). The stability of thiepin (49) results from the 2,7-steric (eclipsed) interactions which obtain in the thianorcaradiene form but which are diminished in the thiepin tautomeric form (relative to the episulfide tautomer). 

Protection of thiols. The r-butyl group has been of limited service for protection of thiols because removal has involved rather drastic treatment with liquid HF. r-Butyl thioethers can be cleaved by treatment with o-nitrobenzene-sulfenyl chloride in acetic acid at 25° to give S-o-nitrophenylsulfeny derivatives. These products are reduced to thiols with NaBH4, HSCH2C02H, or HOCH2CH2SH. 

Photolysis. l-Hydroxy-2-oxindole (162) is reportedly formed from 2-(2-nitrophenyl)ethanol by UV irradiation in several solvents (70ACS2650). The main product of the irradiation of dissolved or powdered 174 is the 1-hydroxyindolone 175, which is formed by the initial attack of the excited nitro group on the r-butyl group (75CB3843). A great deal of mechanistic work has been done on... 

Epoxidation of (Z)-2-methyl-2-hepten-l-ol gave epoxy alcohol 61 (80% yield, 89% ee) [2], of (Z)-2-methyl-4-phenyl-2-buten-l-ol gave 62 (90%, 91% ee) 177], and of (2T)-1 -hydroxy squalene gave 63 (93%, 78% ee) [85]. The epoxy alcohol 64 had >95% ee after recrystallization [91], In the epoxidation of (Z)-2-r-butyl-2-buten-l-ol, the allylic alcohol with a C-2 r-butyl group, the epoxy alcohol was obtained in 43% yield and with 60% ee [38], These results lead one to expect that other 2,3Z-disubstituted allylic alcohols will be epoxidized in good yield and with enantioselectivity similar to that observed for the 3Z-monosubstituted allylic alcohols (i.e., 80-95% ee). 

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