RESUMEN
Asymmetric diboration of terminal alkenes is well established, and subsequent selective functionalization of the less hindered primary boronic ester is commonly achieved. Conversely, selective functionalization of the sterically less accessible secondary boronic ester remains challenging. An alternative way to control chemoselective functionalization of bis(boron) compounds is by engendering different Lewis acidity to the two boryl moieties, since reactivity would then be dictated by Lewis acidity instead of sterics. We report herein the regio- and enantioselective Pt-catalyzed diboration of unactivated alkenes with (pin)B-B(dan). A broad range of terminal and cyclic alkenes undergo diboration to furnish the differentiable 1,2-bis(boron) compounds with high levels of regio- and enantiocontrol, giving access to a wide variety of novel building blocks from a common intermediate. The reaction places the less Lewis acidic B(dan) group at the less hindered position and the resulting 1,2-bisboryl alkanes undergo selective transformations of the B(pin) group located at the more hindered position. The regioselectivity of diboration has been studied by DFT calculations and is believed to originate from the trans influence, which lowers the activation barrier for formation of the regioisomer that places the weaker electron donor [B(pin) vs B(dan)] opposite the strong electron donor (alkyl group) in the platinum complex.
RESUMEN
We computationally study the mechanistic pathway for the synthetically valuable cascading N-H functionalization followed by the C-C bond-forming reaction. The impetus to study such multicomponent reactions catalyzed by Rh(I) arises from the highly fluxional nature of the onium ylide involved, which is often not amenable to experimental detection. Our results throw light on an interesting mechanistic paradigm where the binding of the ylide to the metal plays a crucial role. The study provides some much-needed insights to expand the scope of these highly valuable methodologies to a broader range of asymmetric reactions.
RESUMEN
A facile synthesis of biologically important S-aryl dithiocarbamates has been demonstrated by the aryne three-component coupling involving CS2 and aliphatic amines. This transition-metal-free and mild reaction is scalable and operates with good functional group compatibility. Preliminary mechanistic experiments, including density functional theory studies, are also provided. Moreover, with 3-triflyloxybenzynes, a unique four-component coupling incorporating tetrahydrofuran was observed.
RESUMEN
DFT methods are used to probe the mechanism of a newly developed Ir-quinoid catalyzed C(sp3)-H functionalization of 1,4 dienes. The lowest energy pathway proceeds via an old-school concerted C-H insertion as opposed to a unique hydrogen atom transfer process proposed previously. The concertedness of the reaction shows an intriguing dependence on sterics of the diene leading to either inserted or dehydrogenated products. We use these new insights to tune the axial ligand, and design a more efficient catalyst.