Braun reagent

Deall lation. Chloroformates such as vinyl chloroformates (40) are used to dealkylate tertiary amines. Chloroformates are superior to the typical Von Braun reagent, cyanogen bromide, because of increased selectivity producing cleaner products. Other chloroformates such as aHyl, methyl, phenyl, and trichloroethyl have also been used in dealkylation reactions. Although the dealkylation reaction using chloroformates is mostiy carried out on tertiary amines, dealkylation of oxygen or sulfur centers, ie, ethers or thioethers, can also be achieved. a-Chloroethyl chloroformate [50893-53-3] (ACE-Cl) (41,42) is superior to all previously used chloroformates for the dealkylation reaction. ACE-Cl has the advantage that the conditions requked for ACE... 

One of the virtues of the Braun reagent is that both enantiomers are available, since the chiral diol is made by reaction of phenylmagnesium bromide with (/ )- or (5)-methylmandelate. An application of the (5)-enantiomer is shown in equation (123). The initial aldol reaction was carried out with the magnesium enolate in THF at -78 C to give the diastereomeric aldols in a ratio of 97 3. Transesterification with methanol gives -hydroxy ester (207) in 94% enantiomeric excess. 

H. Waldmann, A. Heuser, P. Braun, M. Schulz, and H. Kunz, in Microbial Reagents in Organic Synthesis, S. Servi, Ed., Kluwer Academic, Dordrecht, 1992, pp 113-122. 

Scheme 6. The von Braun reaction. Reagents a, BrCN, benzene b, BrCN, EtOH or aq THF (MgO).

Braun et al. [258] used a combination of tert-butyllithium (t-BuLi) and tetramefhy-lethylenediamine to create initiator sites at the surface of carbon black for the LASIP of styrene. Schomaker et al. [259] first immobilized a methyl methacrylate derivative on colloidal silica and after activation by a Grignard reagent polymerized MMA. 

Reagent 88 also ranks among the most highly enantioselective chiral acetate aldol enolate equivalents (a) Braun, M. Angew. Chem., Int. Ed. Engl. 1987, 26, 24, and literature cited therein, (b) Masamune, S. Sato, T. Kim, B. M. Wollmann, T. A. J. Am. Chem. Soc. 1986,... 

Additional reagents and equipment for preparation of anthocyanin NMR samples (see Support Protocol 1), recording the 1-D H NMR spectrum (see Support Protocol 2), and recording the 2-D H-13C HMBC, 2-D H-13C HSQC, 2-D H- H DQF-COSY, 2-D H- H TOCSY, 2-D H- H NOESY, and 1-D 13C CAPT spectrums (Braun et al., 1998)... 

M. Braun, a-Heteroatom Substituted 1-Alkenyllithium Reagents Carbanions and Carbenoids for C-C Bond Formation , Angew. Chem. Int. Ed. Engl. 1998, 37, 430 451. 

In a study of the Hofmann-Loffler reaction, the jV-chloro-amine (8a) was irradiated in trifluoroacetic acid solution and underwent photolysis to yield the pyrrolidine (9a) together with the 205-isomer (9b) in a ratio 8 1. The starting amine (8b) was prepared by hydrogenation of (8c), followed by von Braun demethylation and hydrolysis of the JV-cyano-amine (8d) which was so formed. The n.m.r. spectrum of (8b) and of related amines in the presence of lanthanide shift reagents was discussed.10... 

C. The Quaternary Salts and Their Reactions with Nucleophilic Reagents The Hofmann and von Braun Degradations... 

Waldmann H (1988) Liebigs Ann Chem 1175 Waldmann H, Braun P,Kunz H (1991) Biomed Biochim Acta 50 243 Waldmann H, Heuser A, Braun P, SAulz M, Kunz H (1992) In Servi S (ed) Microbial reagents in organic synthesis. Kluwer, Dordrecht, p 113... 

Braun, T., Faiag, A. B. Plasticized open-cell polyurethane foam as a universal matrix for organic reagents in trace element preconcentration I. Collection of silver traces on dithizone foam. Anal Chim. Acta 69, 85 (1974)... 

R5 Braun, H.-P., Carstensen, C.A. and Rittersdorf, W. (1984). Analytical performance of the Refloquant cholesterol reagent carriers compared with the CHOD-PAP method. Clin. Chera. 30, 990-991, Abstr. 259. 

The normal reagent used in the von Braun reaction [e.g. 1320b] with heterocyclic benzamides is PBr ... 

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