Palladium(?)-Catalyzed Aerobic Selective 1,2-Difunctionalization Of Conjugated Dienes

The 1,2-Difunctionalization of conjugated dienes is an important reaction for the functionalization of alkenes.The preserved double bond in the difunctionalized product can be further transformed to give the desired structures or be functionalized sequentially to achieve multi-functionalization.However,mechanistic differences compared to reactions involving isolated alkenes make the difunctionalization more complex.Exisiting problems,such as limited fundamental reaction type,poor atom economy of the oxidant,and selectivitiy issues,must be overcome.To address these issues,we have successfully achieved a 1,2-diamination,1,2-aminooxygenation/1,2-oxyamination and aziridination of conjugated dienes using Pd(?)as catalyst and oxygen as an oxidant.Part I:A Pd(?)-catalyzed aerobic intermolecular 1,2-diamination of conjugated dienes was developed for the selective preparation of a variety of functionalized tetrahydroquinoxalines,using simple sulfonyl protected o-phenylendiamines as a nitrogen source.This methodology provides a direct and efficient synthesis of tetrahydroquinoxalines.Molecular oxygen,as the stoichiometric oxidant,is generally applied to a series of o-phenylendiamines and conjugated dienes.Thirty examples are described,most of them obtaining good yields and selectivities.Part ?:The first Pd(?)-catalyzed intermolecular 1,2-aminooxygenation and1,2-oxyamination of conjugated dienes has been developed.The regiodivergent preparation of a variety of 2-functionalized and 3-functionalized 1,4-benzoxazine derivatives was accomplished via the adjustment of a coordinating solvent.Oxygen was successfully used in this oxidative difunctionalization of alkenes.Good yields and selectivities were obtained for most products.Products bearing a quaternary carbon center or a spiro structure were obtained from a 2,3-disubstituted-1,3-diene.In the case of an(E)-penta-1,3-diene,internal oxyamination of the diene occurred.Origins of the remarkable solvent effect on the chemoselectivity were studied experimentally and via DFT computations.The results indicate that the different coordination modes in Me CN and DMSO solvent are key to regiodivergent aminooxygenations and oxyaminations.Part III:The first Pd(?)-catalyzed aerobic regioselective aziridination of conjugated dienes has been developed using a difunctionalization strategy,differing from commonly used metal-catalyzed aziridinations of alkenes which employ a metal-nitrene process.In our reaction,oxygen has been successfully used as a terminal oxidant in place of the commonly used hypervalent iodine reagents or other strong oxidants which are used in metal-nitrene processes.For most diene substrates,vinyl aziridines bearing large ring-strain and not the five-membered dihydro-pyrroles,were prepared with good yields and regioselectivities.The obtained vinyl aziridines could take part in several useful transformations.Preliminary mechanistic studies indicate that the formation of a?-allyl Pd(?)-intermediate in the difunctionalization of the conjugated diene is favored and that an(E)-iodide intermediate is then most likely formed which undergoes an S_N2'reaction to give the aziridine products.In summary,this thesis describes the 1,2-diamination,1,2-aminooxygenation/1,2-oxyamination and aziridination of conjugated dienes using Pd(?)as catalyst and oxygen as oxidant.Oxygen was used as a terminal oxidant to expand the fundamental transformations capable with conjugated dienes.