ZWITTERIONIC PI-ALLYLPALLADIUM INTERMEDIATES IN PALLADIUM CATALYZED CYCLOADDITION REACTIONS

Abstract

Cycloaddition reactions have been an important topic in organic chemistry since its earliest discovery in the late 19th century. In recent years, the use of zwitterionic π-allylpalladium intermediates in cycloaddition reactions has garnered much attention. Consisting of an electrophilic palladium stabilized π-allyl moiety tethered to either a carbon or heteroatom nucleophile, this transient intermediate, generated in situ from vinyl substrates in the presence of palladium catalyst, has allowed a myriad of (hetero)cyclic structures to be constructed with suitable reaction partners. In this thesis, three projects were carried out using three different precursors that will generate intermediates bearing nitrogen nucleophiles. The first project consists of a highly diastereo- and enantioselective palladium catalyzed [4+2] cycloaddition of vinyl benzoxazinanones to construct [5,6]-spirocycles with a tetrahydrofuran core bearing three contiguous centers. In the second and third projects, benzofuran-fused nine- and ten-membered rings were synthesized in palladium-catalyzed [5+4] and [6+4] cycloadditions respectively. The highlight of these two reactions are employing unprotected vinyl oxazolidinones and vinyl oxazinanones respectively. Different aspects of these works such as preliminary results, optimization of reaction conditions, substrate scope, proposed reaction mechanisms and reaction scale-up will be illustrated.