Bromine with aldehydes

Bromination of aldehydes (qv) is more compHcated because bromination can take place on the aldehyde carbon as weU as the a-carbon. Acetals are brominated satisfactorily in cold chloroform solution in the presence of calcium carbonate, which reacts with the hydrogen bromide formed (24). 

Broadband-decoupled NMR, 451 Bromine, reaction with aldehydes, 846-848... 

Lithium butyldimethylmagnesate was preferable to tributyhnagnesate in the bromine-magnesium exchange of 3-bromopyridine since the latter afforded a rather complex mixture (Table 10)". 2-Bromopyridine and 2-bromothiophene were also converted to the corresponding magnesium reagents which then reacted with aldehydes. 

The mixed 1,2-bimetallic Zn/Si-reagent 47 is a versatile species which reacts with aldehydes in high diastereoselectivity . It is prepared by a bromine/lithium exchange reaction starting from 48 followed by a transmetalation with ZnCl2 (Scheme 21). The... 

A simple method for introducing a triple bond into an organic compound is to treat an appropriate dihalide with a strong base. Since vicinal dihalides (usually the bromide) are readily formed by reaction of bromine with an alkene, and geminal dihalides from aldehydes or ketones with phosphorus pentachloride, the method is a useful general procedure for the preparation of terminal and non-terminal alkynes from readily available starting materials. 

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