A Diels-Alder approach to biaryl synthesis Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5712mb55s

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  • An expedient approach to the synthesis of a wide range of highly programmable biaryl templates has been accomplished. Utilizing the Diels-Alder [4+2] cycloaddition, a wide range of tri- and tetra-ortho-substituted biaryls have been synthesized in only three to four steps from commercially available materials. We have successfully synthesized entire classes of biaryl compounds that would not be readily accessible from alternative methods. In fact, the successful construction of biaryl compounds possessing four different atoms (N, Cl/Br, O and P for the phosphorus series and N, Cl/Br, O and C for the carbonyl and tertiary alcohol series) at the four ortho positions has not been accomplished by any other method. One intriguing feature of these Diels-Alder processes is their ability to construct sterically challenging functionality under mild conditions. In many cases, the cycloaddition sequence appears to work better on the more substituted systems. Additionally, the strong directing ability of the ortho-nitro moiety, even in the presence of ketones, esters and amides is noteworthy. The synthesis of the western biaryl portion of the anti-cancer compound TMC-95 provided the groundwork for our current methodology and is described herein. Also, studies were performed to probe the role of the nitro moiety using both experimental data and molecular modeling calculations. Through a series of phosphorus-containing and carbonyl-containing dienophiles, the scope of the Diels-Alder approach to biaryl synthesis was greatly expanded. The use of ketones, esters, amides and imides led to a wide variety of highly functionalized biaryl compounds. The exploration into propargylic tertiary alcohols as dienophiles in the Diels-Alder reaction proved fruitful as well. A plethora of dienophiles were constructed using a variety of alkyl, aromatic, cyclic and acyclic ketones as electrophiles. Each of the aforementioned compounds underwent smooth cycloaddition and cycloextrusion with a range of mono- and bis-oxygenated dienes to give the highly substituted biaryls in good yields. We have demonstrated the utility of this methodology in designing a highly active catalyst for Suzuki-couplings and Buchwald-Hartwig C-N couplings. Biological application includes preliminary work in the synthesis of axially chiral biaryl amino acids.
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