Date of Award
Doctor of Philosophy
John G. Verkade
In recent years, proazaphosphatranes [P(RNCH2CH2)3N] have proven to be very useful ligands in cross-coupling reactions such as Buchwald-Hartwig aminations, Suzuki-Miyaura couplings, and Stille couplings. In this thesis is described the use of proazaphosphatranes in Lewis base catalyzed reactions such as the synthesis of biaryl ethers by SnAr reactions and the cyclotrimerization of isocyanates to isocyanurates. Recently, our group published the synthesis of a tricyclic aluminum alkoxide Lewis acid. This thesis describes the use of this novel aluminum alkoxide in the catalyzed trimethylsilylcyanation of aldehydes and the Mukaiyama Aldol reaction. The use of tBu3P and the bulky phosphine tBu2P-N=P(iBuNCH2CH2)3N (recently synthesized in our group) in the palladium catalyzed α-arylation of enol silyl ethers and in the Hiyama coupling, respectively, is also described.
This thesis shows that the synthesis of biaryl ethers using P(iBuNCH2CH2)3N as a catalyst under microwave conditions is facilitated at the lowest mole percentage of promoter published in the literature for this SnAr reaction. Herein, it is also shown experimentally that P(BnNCH2CH2)3N is the least basic proazaphosphatrane developed to date, but that the installation of methoxy groups on the phenyl ring markedly increases its basicity. This rise in basicity is shown to increase the rate of cyclotrimerization of isocyanates to isocyanurates.
Lewis acid catalyzed reactions using aluminum as the metal center has advantages (such as low toxicity to the environment and low cost). The chief disadvantage of such catalysts described in the literature is the large concentrations required. The use of a novel tricyclic aluminum alkoxide Lewis acid first synthesized by our group is shown to maintain such advantages while also functioning as an efficient catalyst at unusually low concentrations.
Finally, the efficiency of the palladium/ tBu3P catalyst system for the reaction of enol silyl ethers with aryl bromides and chlorides is found to be drastically increased in the presence of two metal fluoride additives which were found to behave synergistically. In addition, a general method for the Hiyama coupling of aryl bromides and notoriously difficult aryl chloride substrates has been developed using a new bulky phosphine recently synthesized in our group.
Steven Michael Raders
Raders, Steven Michael, "The use of proazaphosphatranes and a tricyclic aluminum alkoxide in organic transformations and the use of bulky phosphines in palladium-catalyzed reactions" (2009). Graduate Theses and Dissertations. 10962.