Hofmann degradation, modifie

Hofmann degradation, styrene 468 was formed. Epoxidation of 468 with m-chloroperbenzoic acid from the less hindered side and lithium aluminum hydride reduction gave ( )-epicorynoline (469). Moreover, slow addition of the a-methoxystyrene 471 to isoquinolinium salt 470 gave cycloadduct 472 in 90% yield. The adduct was hydrolyzed by acid and the resultant aldehyde oxidized to naphthoic acid by Jones oxidation. Modified Curtius rearrangement of 473 with added benzyl alcohol afforded benzyl urethane 474, which was reduced by lithium aluminum hydride and formylated with chloral to give 0-methylarnottiamide (475) (Scheme 60). 

In an investigation of a modified Hofmann degradation, Wittig and Polster found that HBr-elimination from trimethylcyclooctylammonium bromide with phenyllithium gave an olefin mixture containing 80% of c/s-cyclooctene but that with potassium amide in liquid ammonia trans-cyclooctene predominated. 

Modified Hofmann degradation. A suspension of trimethylcyclohexylammonium bromide in an ethereal solution of phenyllithium on being shaken for 72 hrs. at room temperature affords cyclohexene in high yield. A similar degradation of... 

Hofmann degradation gave a methine base, which had only one olefinic proton, and its mass spectrum showed a strong fragment ion [M" "—CHaNMeg]. The methine base must then be either 146 or 147. A second Hofmann degradation product was shown by its NMR spectrum to be l-(2-vinylphenyl)indene derivative 149 but not 148, which implies that the modified Pschorr reaction product has structure 140. 

Ammonolysis of alicyclic anhydrides followed by Hofmann degradation is one of the most frequently used methods for the synthesis of alicyclic P-amino acids, since many anhydrides are commercially available cheap substances produced by Diels-Alder addition of maleic anhydride and the corresponding dienes [44], By this method, cis- and frans,-2-aminocyclohexane- and -cyclohexenecarboxylic acids, cis-2-aminocycloheptanecarboxylic acid [45], 3-ewtffo-aminobicyclo [2.2.1 ]heptane-2-ew/o-carboxylic acid, 3-e ifo-aminobicyclo[2.2.1 ]hept-5-ene-2-ertcarboxylic acid and some analogue P-amino acids have been prepared [44, 46-48], For partially unsaturated alicyclic compounds, a modified Hofmann degradation is used, sodium hypochlorite being applied to avoid bromine addition to the double bond [48,49]. 

The parent system (28, R = H) serves as a building block, e.g. for polyheterocyclic systems (see p 474). It is commercially produced by a modified Hofmann degradation of phthalimide. 

Dihydrokoumine (33) was first isolated as a natural product (36), although it has been prepared reductively from koumine (29) during the structure elucidation of 29 (37). The H- and 13C-NMR spectral assignments of 33 were reinvestigated. In this report, the result of modified Hofmann degradation of koumine derivative (35) was presented (Fig. 7). The structure and stereochemistry of the main product (36) (15-20% yield) were deduced by spectral methods and confirmed by X-ray diffraction analysis. 

Dihydrokoumine (74) was isolated as a natural product 42), although it had been prepared from koumine (70) during its structure elucidation 43). In this report, modified Hofmann degradation of koumine derivative was also described. 

Benzyltrimethylammonium tribromide j sodium hydroxide Modified Hofmann degradation under mild conditions... 

Modified Hofmann degradation of quaternary ammonium salts... 

The halide-containing (co)polymers, such as PVC or PVDC, recovered from commingled polymer scrap were contaminated by low melting point PA S [e.g., PA-6, PA-1212 or PARA]. The recyclate was compatibilized and impact modified by addition of an acrylic copolymer of ethylene, alkyl(meth)acrylate, vinylacetate, (meth)acrylic acid, CO and MA. To prevent degradation, the blends were processed at T < 220°C, then formed by extrusion or injection molding into a variety of articles [Hofmann, 1994]. 

The onset temperature of decomposition of alkyl quaternary ammonium-modified montmorillonite, in nonoxidative thermal degradation, is about 180°C. Initial degradation of the surfactant follows either a Hoftnann elimination or an Sn2 nucleophilic substitution mechanism. Both mechanisms can affect the performance of high-processing-temperature nanocomposites and, in general, the thermal stability and combustion behavior of nanocomposites. In particular, Hofmann elimination generates acidic sites on the layered silicate that can act as a protonic acid catalyst on polymer decomposition. " Imidazolium and phosphonium salts exhibit improved thermal stability compared to ammonium salts.Alkylimidazolium salt-modified layered silicates were used successfully to prepare organoclays that exhibit an onset of decomposition temperature up to 392°C. 

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