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The acidic hydrogen on terminal alkynes can be replaced by a variety of groups resulting in halo-, silyl-, and alkoxoalkynes. The carbanions generated by deprotonation of terminal alkynes are called acetylides. [5] Internal alkynes are also considerably more acidic than alkenes and alkanes, though not nearly as acidic as terminal alkynes.
Hydroaluminations of terminal alkynes typically produce terminal alkenylalanes as a result. Selectivity in hydroaluminations of internal alkynes is typically low, unless an electronic bias exists in the substrate (such as a phenyl ring in conjugation with the alkyne). [9] (2)
Disiamylborane is relatively selective for terminal alkynes and alkenes vs internal alkynes and alkenes. Like most hydroboration, the addition proceeds in an anti-Markovnikov manner. [1] It can be used to convert terminal alkynes, into aldehydes. The hydroboration process proceeds via an initial dissociation of the dimer. [2]
The azide-alkyne Huisgen cycloaddition is a 1,3-dipolar cycloaddition between an azide and a terminal or internal alkyne to give a 1,2,3-triazole. Rolf Huisgen [ 1 ] was the first to understand the scope of this organic reaction .
These steps will be repeated, essentially moving the alkyne along the alkane chain until a terminal alkyne is achieved. [3] Once a terminal alkyne is achieved, the 3-aminopropylamine anion will attack and remove the terminal proton. However, the process stops there because the carbon-hydrogen bond electrons cannot form an additional pi-bond on ...
The Seyferth–Gilbert homologation is a chemical reaction of an aryl ketone 1 (or aldehyde) with dimethyl (diazomethyl)phosphonate 2 and potassium tert-butoxide to give substituted alkynes 3. [1] [2] Dimethyl (diazomethyl)phosphonate 2 is often called the Seyferth–Gilbert reagent. [3] The Seyferth–Gilbert homologation
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A hydroboration reaction also takes place on alkynes. Again the mode of action is syn and secondary reaction products are aldehydes from terminal alkynes and ketones from internal alkynes. In order to prevent hydroboration across both the pi-bonds, a bulky borane like disiamyl (di-sec-iso-amyl) borane is used. [5]