Asymmetric nucleophilic boronate reactions have been developed using organic chiral diols, specifically binaphthols, as catalysts. A highly enantioselective allylboration of acyl cyanides under solvent-free conditions was catalyzed by (S)-Br2BINOL. The reaction proceeds through single exchange of boronate with the chiral catalyst, promoted by tert-butanol. Allylation products were obtained in yields up to 97% and enantioselectivities up to 99:1 er. Syn- and anti-crotylborations of benzoyl cyanide were also performed, and the corresponding a-methyl products were isolated in good yields and moderate to good enantioselectivities, with the E-boronate producing a single diastereomer. This methodology represents a new route to enantioenriched homoallylic cyanohydrins through nucleophilic addition of the allyl group to acyl cyanides.
The enantioselective Petasis reaction of glycolaldehyde dimer to synthesize b- amino alcohols was also investigated. With commercially available aldehyde dimer, boronic acids, and amines, electron-rich a-arylglycinols were obtained in up to 92% yield and up to 99.5:0.5 er. Direct inject mass spectrometry studies revealed a single exchange between p-methoxyphenylboronic acid and (S)-Br2BINOL, as well as coordination of the imine intermediate to the catalyst-boronate complex. This reaction was further optimized to include electron-deficient boronic acids. Addition of Lewis acidic triethylborate had a two-fold effect on the reactivity; it facilitated both the exchange of boronic acid with catalyst, and the formation of the imine intermediate. Using chloroform as the solvent, and (S)-Ph2BINOL, halogenated phenylboronic acids participated well in the Petasis reaction. This methodology is the first asymmetric Petasis reaction of glycolaldehyde to produce b-amino alcohols. / 2018-12-06T00:00:00Z
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/19734 |
| Date | 07 December 2016 |
| Creators | Summo, Kathryn Eva |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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