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Disiamylborane is prepared by hydroboration of trimethylethylene with diborane. [1] The reaction stops at the secondary borane due to steric hindrance. 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]
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]
This process utilizes anti addition of an OH group to the more substituted carbon, making this reaction a Markovnikov reaction. Alkyne hydroboration-oxidation: In this reaction, a disiamylborane reaction, disiamylborane is added to one face of the triple bond. The boron atom attaches to the less substituted carbon, and later forms a bond ...
The stereochemistry is cis-addition. With terminal alkynes, both H 2 BCH=HR and HB(CH=CHR) 2 are formed. Often the hydroboration of alkynes use bulky boranes such as 9-BBN to give monoalkenylborane products. The alkenylboranese are susceptible to many reactions such as protonolysis to give the alkene and oxidation to give the aldehyde or ketone ...
It reacts only slowly with simple terminal alkenes. It adds to alkynes to give alkenylboranes. [11] Among hindered dialkylboranes is disiamylborane, abbreviated Sia 2 BH. It also is a dimer. Owing to its steric bulk, it selectively hydroborates less hindered, usually terminal alkenes in the presence of more substituted alkenes. [12]
The alkyne zipper reaction is an organic reaction that involves isomerization of a non terminal alkyne into a terminal alkyne. This reaction was first reported by Alexey Favorsky in 1887 (J. Russ. Phys.-Chem. Soc., 19, 414 (1887)). Also, this reaction was reported by Charles Allen Brown and Ayako Yamashita in 1975. [1] The isomerization ...
Reactions of alkenyl- and alkynylaluminium compounds involve the transfer of a nucleophilic alkenyl or alkynyl group attached to aluminium to an electrophilic atom. Stereospecific hydroalumination, carboalumination, and terminal alkyne metalation are useful methods for generation of the necessary alkenyl- and alkynylalanes.
Meyer-Schuster Rearrangement. The reaction mechanism [5] begins with the protonation of the alcohol which leaves in an E1 reaction to form the allene from the alkyne.Attack of a water molecule on the carbocation and deprotonation is followed by tautomerization to give the α,β-unsaturated carbonyl compound.