Transition metal-catalyzed oxidative annulations of o-alkenylphenols

Zusammenfassung

In my report of investigation are collected the results of my studies on annulations based on C-H activation of ortho-alkenylphenols with allenes or alkynes catalyzed by complexes of Rh (III) and Pd(II) that has lead to the formation of interesting products as spirocyclic, cromens and benzooxepines. • The first chapter of my thesis is a Rhodium(III)-Catalyzed Dearomatizing (3 + 2) Annulation of 2-Alkenylphenols and Alkynes. It is published JACS, 2014, 136, 7607-7610. We have developed a new type of metal-catalyzed[3C+2C] cycloaddition that can be considered “anomalous” interms of classical reactivity, as it involves the dehydrogenative cleavage of an O−H and a C−H bond, as well as a dearomatization of a phenyl ring. The reaction allows transforming extremely simple substrates into attractive, chiral spirocyclic products featuring an interesting array of substituent son olefin positions. The reaction proceeds in an atom economical manner and takes place with excellent chemo- and regioselectivity. Our results point out the potential of using substituents in key strategic positions of substrates to changereaction outcomes (oxepine vs spirocycle) because of the generation of steric interferences that affect key steps of the mechanism. Finally, preliminary results suggest that the spirocyclic products can be thermolyzed to interesting azulenone products. • The second chapter of my thesis is a Rhodium-Catalyzed (5+1) Annulations Between 2-Alkenylplenols and Allenes: A Practical Entry to 2,2-Disubstituted 2H-Chromenes. It is published Angew. Chem.2015, 127, 1-5. In this case, we have described a new rhodium-catalyzed oxidative annulation formally involving the cleavage of the C-H and O-H bond of 2-alkenylphenols. Key for the success of the reaction is the use of allenyl derivatives as reaction partners. The transformation proposes a straightforward, atom-economical access to highly appealing chromene skeletons,is operationally simple, permits use of non-dried solvents and air, and requires trivial starting materials. The reaction proceeds through an intriguing sequential mechanism involving an initial rhodium(III)-catalyzed addition by a [1,7] sigmatropic hydrogen shift and a 6π-electronelectrocyclic ring closure. • The last chapter of my thesis work is a Palladium (II)-Catalyzed Annulation between ortho-Alkenylphenols and Allenes. Key Role of the Metal Geometry in Determining the Reaction Outcome. It is published ACS catal. 2016, 6, 3349. Finally,we have developed a straightforward and selective access to a wide range of benzoxepine skeletons through a palladium-catalyzed (5 + 2) formal cycloaddition involving a C−H activation process. This is one of the scarce examples of annulations based on the cleavage of γ−C−H bonds which involve the use of allenes, as well as one of the very few leading to seven-membered rings. Remarkably, themethod has a much higher scope with respect to both, the alkenyl phenol component and the allene, than the rhodium catalyzed annulations, and even allows the formation of cycles with tetrasubstituted carbons. Computational studies support the hypothesis that the different course of the reaction promoted by Pd(II) or by Cp*Rh(III) catalysts can be ascribed to the geometric requirements associated with their respective square planar or a pseudo-octahedral geometries.