Elimination, of hydrobromic acid from

Elimination, of hydrobromic acid from a dibromide, 22, 50 of hydrobromic acid from a dibromide with rearrangement, 24, 33 Emulsin, 22, 53 Enzymatic synthesis, 22, 53... 

The addition of ammonia to these substrates occurs via A-attack at the S7-face of C-3, with protonation occurring from the 7 e-face of C-2, yielding the functionalized aspartic acid having the (27 ,3S)-configuration40 b. The absolute configuration of the chloroaspartic acid was determined by reduction (H2/Pd - C) to L-aspartic acid ([a]D + 21.5), and by two-step conversion to (Z)-2-chloro-2-butenedioic acid (diazotization in the presence of the bromide ion with retention of configuration, followed by elimination of hydrobromic acid from the intermediate 2-bromo-3-chlorosuccinic acid). 

Bromopropylene, CH2 = CBr.CH3, (b.p. 48°), like other substances of this class, can be prepared from a halogen derivative of a saturated hydrocarbon, by applying the general method of preparing unsaturated compounds. It is formed from the dibromopropane of the structure CH3.CBr2.CH3 by eliminating one molecule of hydrobromic acid —... 

In the first step the diethyl ester of malonic acid is treated with ethyl bromide in the presence of sodium ethoxide when one of the active hydrogen atoms in the former gets eliminated with bromine atom in the later as a molecule of hydrobromic acid resulting into the formation of the corresponding diethyl ester of ethyl malonic acid. This on subsequent addition of 2-monobromopentane and in the presence of sodium ethoxide gives rise to diethyl ether of ethyl-(l-methyl butyl) malonate with the elimination of one molecule of hydrobromic acid. Urea is made to condense with the product obtained from the previous step when pentobarbital is formed with the elimination of two moles of ethanol. Finally, the pentobarbital is treated with a calculated amoimt of sodium hydroxide when the required official compoimd is formed. 

Brown s result was supported by later experiments in which bromonium ions were generated by bubbling gaseous hydrobromic acid through a solution of bromohydrins in halogenated solvents. Under these conditions, bromine is eliminated as it is formed, so that the resulting alkene is observed directly (Scheme 15). This method has been applied to the bromohydrins derived from cis- and trans-stilbenes (Scheme 16) and from 5//-dibenzo[a,d]-cycloheptene and -azepine systems ([29a] and [29b] respectively Scheme 17), in which steric constraints should favour elimination (path a) as against substitution (path b). 

Cyclic orthoesters derived from gem-diols offer a further route to alkenes. As part of a three-step conversion, they may be ring opened with hydrobromic acid to give O-acyl bromodeoxy compounds that undergo reductive elimination with copper-zinc. In this way, unsaturated nucleosides have been made by way of mixed 2y3,-bromo-2y3,-deoxy-3,/2, carboxyl-ates.174 A more direct route to alkenes from cyclic orthoesters involves heating in acetic anhydride together with zirconium oxide.175... 

Triethylarsine dibromide, (C3H5)3AsBrj.— Triethylarsine sulphide is treated with concentrated hydrobromic acid, or triethylarsine with bromine in alcoholic solution. It crystalli.ses from chloroform in deliquescent needles, easily soluble in water and alcohol, insoluble in ether. Chlorine or nitric acid eliminates the bromine, and with concentrated sulphuric acid decomposition takes place with evolution of hydrogen bromide. 

Hydriodic acid and phosphorus (22), like hydrochloric or hydrobromic acid replaces the hydroxyl of tropine by a halogen atom. The reductive elimination of this iodine atom from iodotropane by nascent hydrogen (Zn + HCl) provided the first preparation of the parent substance, tropane (dihydrotropidine) (I, R = CH3). (A more direct preparation of tropane is by the catalytic reduction of tropidine over platinum black (159a)). Tropane reacts readily with hydrogen chloride at an elevated temperature eliminating methyl chloride with the formation of a new saturated base, nortropane (94). The methyl group eliminated from tropane must have been attached to the nitrogen, for nortropane, in contrast to tropane, forms a well defined A-nitroso derivative. The isolation of methyl chloride and the secondary amine, nortropane, confirms the earlier assumption of the... 

Vinylamine, CH2 = CH.NH2, is an example of an amine which contains an unsaturated radical. It is made by an application of the general methods used in preparing unsat- urated compounds. When bromoethylamine is heated with a solution of potassium hydroxide, hydrobromic acid is eliminated from the saturated compound —... 

Vinylselenonium salts derived from selenolane were obtained by hydrobromic acid elimination from 8-bromoalkylselenonium salts <88ZOR355>. Generation of dinitrocarbene is possible through electrochemical oxidation of the ylide (20) <89IZV356>. 

An easy and efficient one pot synthesis of peracetylated glycals from unprotected sugars has been described. In this method the sugar was sequentially treated with acetic anhydride and catalytic hydrobromic acid-acetic acid (to effect per-acetylation), more hydrobromic acid-acetic acid (to form the glycosyl bromide), sodium acetate (to neutralize excess hydrobromic acid) and finally a buffered mixture of sodium acetate, acetic acid, zinc-copper sulfate and water (to effect a reductive-elimination). The method was applied to the syntheses of glycals derived from D-glucose, D-galactose, L-rhamnose, L-arabinose, maltose, lactose and maltotriose. ... 

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