Bromides, acid complex

It was found that 2-propenyloxymagnesium bromide reacts much more readily with nitrile oxides than other known dipolarophiles of electron-deficient, electron-rich, and strained types, including 3-buten-2-one, ethyl vinyl ether, and norbomene, respectively (147). Therefore, this BrMg-alkoxide is highly effective in various nitrile oxide cycloaddition reactions, including those of nitrile oxide/Lewis acid complexes. 

In the presence of an electrophile, tautomerization of a substrate with a C=0 double bond to its enol only takes place when catalyzed by either a Bronsted- or a Lewis acid. The proton-catalyzed mechanism is shown for the ketone — enol conversion B — iso-B (Figure 12.4), the carboxylic acid —> enol conversion A — E (Figure 12.6), the carboxylic acid bromide — enol conversion E —> G (Figure 12.7) and the carboxylic acid ester — enol conversion diethyl-malonate —> E (Figure 12.9). Each of these enol formations is a two-step process consisting of the protonation to a carboxonium ion and the latter s deprotonation. The mechanism of a Lewis acid-catalyzed enolization is illustrated in Figure 12.5, exemplified by the ketone —> enol conversion A —> iso-A. Again, a protonation to a carboxonium ion and the latter s deprotonation are involved the Lewis acid-complexed ketone acts as a proton source (see below). 

A later modification of the original KObrich procedure entails the generadon of carbenoids in the presence of an added equivalent of lithium bromide salt (equadon 22). Appaiendy, the Lewis acid character of the added s t helps to stabilize the carbenoid by coordination widi the hdogen atom. The lithium salt is also implicated in Lewis acid complexation to the oxygen atom of the C=0 bond, and seems to assist in the cyclization step as well. 

Because of its similarity to trimethylamine oxide, the ylid may be considered as a Lewis base, and, as such, it should coordinate with various Lewis acids. Complexes with lithium bromide and trimethylbromostannane have already been mentioned and it would be expected that coordination with boranes and alanes would also give stable products. 

Allyl bromide 1-Propene, 3-bromo- (106-95-6), 76, 60, 221 L-ALLYLGLYCINE 4-PENTENOIC ACID, 2-AMINO-, (R)- (54594-06-8), 76, 57 Allylic alcohols, enantioselective cyclopropanation, 76, 97 Allylmagnesium bromide Magnesium, bromo-2-propenyl- (1730-25-2), 76, 221 Allylmagnesium bromide (ethereal complex solution), 76, 221 Allylmagnesium bromide (THF complex solution), 76, 222 Allyltributylstannane Stannane, tributyl-2-propenyl- (24850-33-7), 75,12... 

Octyne and 2-octyne also give more than 95% anti addition under these conditions. The reactions are formulated as concerted Ad S processes, involving bromide attack on an alkene-acid complex. 

Inorganic Derivatives. - The copper(II) - 2-carboxypentonic acid complex ([Cu9Br2(cpa)6] .xH20) formed from copper(II) bromide and L-ascorbic acid. ... 

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