Dibutyl acetyleneboronate

Like their aryl and alkenyl counterparts, alkynylboronic adds can be made by displacement of magnesium or lithium acetylides with borate esters. For example, Mat-teson and Peacock have described the preparation of dibutyl acetyleneboronate from ethynylmagnesium bromide and trimethyl borate [294]. The C-B hnkage is stable in neutral or acidic hydrolytic solvents but readily hydrolyzes in basic media such as aqueous sodium bicarbonate. Brown and co-workers eventually applied their organo-lithium route to boronic esters to the particular case of alkynylboronic esters, and in this way provided a fairly general access to this class of compounds [295]. 

Dibutyl acetyleneboronate is a moderately active dienophile since the Diels-Alder adduct with cyclopentadiene was obtained in a 25% yield after heating at 130 °C for 15 h [62]. In contrast, alkynyldibromoboranes, generated in situ by silicon/boron exchange, appeared to be highly reactive dienophiles [63]. Unfortunately, their great electrophilidty restricted their synthetic application to unfunctionalized substrates. 

A mixture of dibutyl acetyleneboronate and bromotrichloromethane heated 2.5 hrs. at 95° under Ng in the presence of a little azodiisobutyronitrile added in 2 portions dibutyl 3,3,3-trichloro-l-bromopropene-l-boronate. Y ... 

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See also in sourсe #XX -- [ ]

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