Reported herein is a brief summary of the history,
properties, and applications of amine-boranes. The past methods devised for
their preparation are described and the routes used to produce the compounds
used in the work presented here are detailed. Building on prior synthetic
approaches to amine-boranes, a new carbon dioxide mediated synthesis is
presented. Proceeding through a monoacyloxyborane intermediate, the borane
complexes of ammonia, primary, secondary, tertiary, and heteroaromatic amine
are provided in 53-99% yields. Utilizing the amine-boranes obtained from the
methods described, two divergent methods for direct amidation are introduced.
The first uses amine-boranes as dual-purpose reagents, where the carboxylic
acid is first activated by the borane moiety to form a triacyloxyborane-amine
complex. This allows the delivery of the coordinated amine to form the amide
products. A series of primary, secondary, and tertiary amides were prepared in 55-99% yields using this protocol, which
displays a broad functional group tolerance. Extended from this dual-purpose
methodology, a catalytic amidation is described. Utilizing ammonia-borane as a
substoichiometric (10%) catalyst, a series of secondary and tertiary amide are
prepared directly from carboxylic acids and amines in 59-99% yields, including
amines containing typically borane reactive functionalities including alcohols,
thiols, and alkenes. Amine-boranes are additionally used in two borylation
methodologies. By reaction with <i>n</i>-butyl lithium, the amine-boranes are
converted to the corresponding lithium aminoborohydrides, which upon reaction
with a terminal alkyne provides the alkynyl borane-amine complexes in 65-98%
yields. This process is compatible with both alkenes and internal alkynes, as
well as a range of aprotic functionalities. A new strategy for aminoborane
synthesis is also described and applied to the borylation of haloarenes.
Activation of a series of amine-boranes with iodine produces the iodinated
amine-borane, which undergoes dehydrohalogenation with an appropriate base to
produce either monomeric or dimeric aminoboranes. Several aminoboranes were
synthesized exclusively as the monomeric species, which due to their greater
reactivity, were used directly in the synthesis of a series of aryl boronates
in 65-99% yields.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14519439 |
| Date | 30 April 2021 |
| Creators | Henry J Hamann (10730742) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Amine-Boranes_Synthesis_and_Applications/14519439 |
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