Jimmie D. Weaver

Transition Metal-Catalyzed Decarboxylative Allylation and Benzylation Reactions

A review. Transition metal catalyzed decarboxylative allylations, benzylations, and interceptive allylations are reviewed.

Facile Synthesis of Z-Alkenes via Uphill Catalysis

Catalytic access to thermodynamically less stable Z-alkenes has recently received considerable attention. These approaches have relied upon kinetic control of the reaction to arrive at the thermodynamically less stable geometrical isomer. Herein, we present an orthogonal approach which proceeds via photochemically catalyzed isomerization of the thermodynamic E-alkene to the less stable Z-isomer which occurs via a photochemical pumping mechanism. We consider two potential mechanisms. Importantly, the reaction conditions are mild, tolerant, and operationally simple and will be easily implemented.

Photocatalytic Hydrodefluorination: Facile Access to Partially Fluorinated Aromatics

Polyfluorinated aromatics are essential to materials science as well as the pharmaceutical and agrochemical industries and yet are often difficult to access. This Communication describes a photocatalytic hydrodefluorination approach which begins with easily accessible perfluoroarenes and selectively reduces the C-F bonds. The method allows facile access to a number of partially fluorinated arenes and takes place with unprecedented catalytic activity using a safe and inexpensive amine as the reductant.

Stereospecific Decarboxylative Allylation of Sulfones

Allyl sulfonylacetic esters undergo highly stereospecific, palladium-catalyzed decarboxylative allylation. The reaction allows the stereospecific formation of tertiary homoallylic sulfones in high yield. In contrast to related reactions that proceed at -100 degrees C and require highly basic preformed organometallics, the decarboxylative coupling described herein occurs under mild nonbasic conditions and requires no stoichiometric additives. Allylation of the intermediate alpha-sulfonyl anion is more rapid than racemization, leading to a highly enantiospecific process. Density functional theory calculations indicate that the barrier for racemization is 9.9 kcal/mol, so the barrier for allylation must be <9.9 kcal/mol.

Catalytic enantioselective protonation of nitronates utilizing an organocatalyst chiral only at sulfur.

The highly enantioselective protonation of nitronates formed upon the addition of α-substituted Meldrums acids to terminally unsubstituted nitroalkenes is described. This work represents the first enantioselective catalytic addition of any type of nucleophile to this class of nitroalkenes. Moreover, for the successful implementation of this method, a new type of N-sulfinyl urea catalyst with chirality residing only at the sulfinyl group was developed, thereby enabling the incorporation of a diverse range of achiral diamine motifs. Finally, the Meldrums acid addition products were readily converted to pharmaceutically relevant 3,5-disubstituted pyrrolidinones in high yield.

Dual C–F, C–H Functionalization via Photocatalysis: Access to Multifluorinated Biaryls

Multifluorinated biaryls are challenging to synthesize and yet are an important class of molecules. Because of the difficulty associated with selective fluorination, this class of molecules represent a formidable synthetic challenge. An alternative approach to selective fluorination of biaryls is to couple an arene that already possesses C-F bonds in the desired location. This strategy has been regularly utilized and relies heavily on traditional cross-coupling strategies that employ organometallics and halides (or pseudohalides) in order to achieve the coupling. Herein we report conditions for the photocatalytic coupling via direct functionalization of the C-F bond of a perfluoroarene and C-H bond of the other arene to provide an expedient route to multifluorinated biaryls. The mild conditions and good functional group tolerance enable a broad scope, including access to the anti-Minisci product of basic heterocycles. Finally, we demonstrate the value of the C-F functionalization approach by utilizing the high fluorine content to systematically build complex biaryls containing between two and five Caryl-F bonds via the synergistic use of photocatalysis and SNAr chemistry.

Photoredox-Mediated C–H Functionalization and Coupling of Tertiary Aliphatic Amines with 2-Chloroazoles

Herein, conditions for C-H functionalization of tertiary aliphatic amines and their subsequent coupling with a number of 2-chloroazole derivatives are reported. The reaction is facilitated by a catalytic amount of tris-fac-Ir(ppy)3, with blue light irradiation and takes place under mild and convenient conditions. Most couplings take place with excellent regioselectivity. The reaction is tolerant of a number of functional groups and allows for rapid access to α-azole carbinamines commonly found in post-translationally modified peptides.

Decarboxylative Allylation using Sulfones as Surrogates of Alkanes

Alpha-sulfonyl functional groups are traceless activating groups that facilitate catalytic decarboxylative allylations in high yield yet can be cleaved to allow the synthesis of simple allylated alkanes. Substrate studies suggest that decarboxylation to form an alpha-sulfonyl anion is rate-limiting. Furthermore, the anion is formed regiospecifically under formally neutral conditions.

Reductive Alkylation of 2-Bromoazoles via Photoinduced Electron Transfer: A Versatile Strategy to Csp2–Csp3 Coupled Products

Access to Csp(2)-Csp(3)-coupled products is a challenging goal at the forefront of catalysis. The photocatalytic reductive coupling of aryl bromides with unactivated alkenes is introduced as a convenient method that circumvents any need for synthesis of sp(3)-hybridized coupling partners. The reaction takes place via photoinduced electron transfer from a tertiary amine to an aryl bromide that fragments to provide an aryl radical and subsequently reacts with an alkene to form a C-C bond. Conveniently, the amine also serves as the final reductant. The method is operationally simple, functional group tolerant, and takes place with selectivities that will allow it to be used in the context of complex molecule synthesis.

Photocatalytic Generation of 2-Azolyl Radicals: Intermediates for the Azolylation of Arenes and Heteroarenes via C–H Functionalization

The 2-azolyl radical, generated from 2-bromoazoles via photocatalysis, is a powerful intermediate for the intermolecular arylation of unmodified (hetero)arenes. The reaction is characterized by mild conditions, operational simplicity, tolerance toward functional and sterically demanding groups, broad scope, and anti-Minisci selectivity. A working mechanism is provided, and a low-solubility amine is essential for successful coupling. The utility of the reaction is demonstrated via late-stage functionalization of methyl estrone and application toward other bromoarenes.