Description
Here, two substituent groups were transferred from a single trialkylborane; one group to each of two equivalents of p-benzoquinone. The synthesis of trialkyl boranes using BCl₃ was explored, and the Matteson procedure for hydroborations with BCl₃ was successfully modified to make dialkylmonochloroboranes. The resulting monochloroboranes were methylated with either MeMgBr, or dimethylzirconocene to synthesize mixed alkylboranes. The migratory aptitude of a borane's substituents was established, in order: secondary, primary, methyl, phenyl. Due to the methyl group's size, migratory aptitude, and synthetic ease of use, it became the preferred borane auxiliary. The purity of these mixed alkylboranes was examined through a procedure developed by the Cole Group. A system of standardized solutions sealed in capillary tubes for use during NMR spectroscopic analysis was developed; e.g., the BF₃·OEt₂ standard derived a known, reproducible resonance signal from which the other signals could be plotted during the 11B NMR analyses. In turn, upon introduction of a complexation reagent, precise separations of isomeric products can be identified and quantified. Next, methylation of various borinic esters was explored. Upon isolation, the newly formed mixed alkylboranes were found to behave the same as directly synthesized boranes. Thus, the utility of a borane that could be extended beyond the transfer of a single alkyl group under different synthetic circumstances was established. Water in the reaction system was determined to effectively prevent transfer of the second group; yet, it did not interfere with transfer of the first group. Mixed alkylboranes were used to perform reductive alkylations of p-benzoquinone in solutions of Et₂O, THF, pentane, water, and combinations thereof to explore the role solvent effects had upon the reductive alkylation reactions. A novel preparation of boronic acids suitable for various subsequent uses was developed.
